Title: Killer Instinct
Pairing: Grimmjow/Ichigo
Rating: M
Genre: Angst, dark, psychological(?)
Disclaimer: I do not own BLEACH nor am I profiting from this fic in any way. Gore.
Synopsis: AU. Ichigo is a young detective with his own personal demons who was picked to join the homicide team for a serial murder case to hunt down the killer known as the 'Rokuban Killer'. He soon finds out that the both of them shared more things in common than he thought and faces a lot of conflict both inside and around him.

Written out of impulse! So excuse me if there are any mistakes regarding the terms and police stuffles… Watching a lot of CSI and Criminal Minds still doesn't help x'D For those parts I don't know the process… well I tried to use my imagination and common sense lol. And yes I am attempting to juggle this with Blue Thread of Fate and Compensation.

An attractive blue-haired man, dressed in a dark grey hoodie and navy undershirt, was sitting alone at a table in a crowded bar. The bar was dimly lit, with the music from the jukebox drowned by the crowd's chatter. He was staring at another man at the other end of the bar. The man was younger, fit and looked like the type who did sports. The younger man hadn't noticed him – couldn't notice him among the crowd. The blue-haired one slowly finished his drink before making his way to the man.

"Hey, ya alone?" He struck a conversation easily with smooth and innocent words.

"Yeah, just wanted to drink," the guy replied and smiled the moment he took in the other's features. "You?"

"Same here," the blue-haired man responded with a charming grin. "Say, do ya work out or do some fighting? Ya got some pretty nice muscles there." The blue-haired man asked and his bright blue eyes raked over the other man's arms. The younger man grinned at him and touched his arm indiscreetly.

"Yeah, some boxing. Think I'm pretty good at it too. Won some medals in some minor competitions," the nameless man said smugly and mocked a stance. "Ya like fighting?"

"Love it," the blue haired man replied with a glint in his eye.

The younger man seemed to appreciate the company, but the blue-haired one had other ideas. He can tell what kind of work one does from the shape of their body. The structure, the built, the muscles. From all that boxing training that the young man boasted, he could see that he really did work out a lot. The blue haired man smiled; this man was the right one.

He then leaned forward to speak into the nameless one's ear, "Wanna go some place quiet? It's too crowded and noisy here." The blue-haired man leaned a little closer, lips touching the other's ear while he placed his hand on his shoulder, and the younger man seemed to lose his breath.

"Yes," the younger man replied breathily. The blue-haired man grinned. Too easy. He stood up and headed for the exit, knowing that the young man would follow him.

Strangely, no one noticed the blue panther that was leading his next prey out the door.

-xxxxxxxxxxxxx-

Kurosaki Ichigo grumbled to himself when he was roused from his much needed sleep by the ringing of his cell phone. He looked at his clock. 6:15 am. Running a hand through his orange hair, he picked the phone up grudgingly, and managed to stop himself from snapping at the person on the other line.

"Kurosaki-san? I think we have a new one here," Urahara's annoying sing-song voice spoke to him through the phone's receiver. Ichigo sighed. Another one already? What the hell, Ichigo thought, he just solved one murder case earlier, which he was trying to recover some sleep from. "This time it's a pretty big case… We have a serial killer."

Ichigo immediately perked up at that and uttered his reply. His captain aka boss continued by telling him the address and hung up, his unsaid words already pushing Ichigo off his bed so that he could get to the crime scene as soon as possible. Good thing it wasn't that far off from his place. He quickly went to wash his face and slip on his pants before grabbing his badge and coat and heading out his small apartment door. Giving out another sigh, Ichigo ran down the stairs and readied himself for a major case.

When he finally reached the crime scene half an hour later, there was a small group poking their noses around the police tape which blocked the entrance of a narrow alley, where the police officers vainly kept on informing them to back away. It was a small, shady part of Karakura and it was early in the morning, so fortunately they didn't get that much attention. Ichigo hated going through crowds of on-lookers just to get to the police tape. The orange-haired man gingerly walked past the people, ducked under the tape and flashed his badge to the crowd controlling officer before he proceeded to meet the sandy-haired man who was standing by the covered body. The CSIs were already there examining the area.

"Urahara-san," Ichigo greeted. The man turned to him, his face looking a little haggard than he had seen him before. His stubble had grown and he had darker circles round his eyes. "I think you need more sleep."

"I think we all need more sleep," Urahara replied him with a tired grin. Ichigo could only agree. He himself had barely gotten an hour of sleep before Urahara had rung him up for this case. Urahara nodded to the direction of the covered body and filled Ichigo in. "Motorist walked here to take a piss, saw the body… wet his pants instead and called the cops."

"That bad huh?" Ichigo asked. Without waiting for a reply, he knelt down and took a peek under the cover, and what he saw sent him backing up and suppressing the bile in his throat. "Fuck!"

"Yeah, that's what the cover was for," Urahara said with an amused smirk.

"Ugh, I can take it… Just that it was kinda sudden… Didn't expect it to be that bad," Ichigo said with a deeply disgusted frown and calmed his nerves. "How long has he been dead? And cause of death?"

"The coroner said approximately six or seven hours," Urahara replied. "And a slash to the throat." Ichigo nodded, still trying to recuperate from the shock.

After a minute he walked back to the body of the victim – male – which was laying on his stomach but his head was facing to the side with lifeless eyes wide open from what seemed like shock. He was also covered in bruises, along with a deep large slash that traced the middle of the neck. What sent bile up his throat wasn't that but the large gaping hole in the lower part of the man's stomach. The insides were cleaned out; the stomach and intestines were gone. It was almost expertly done, probably practiced even. Ichigo felt a strange feeling rising inside him but ignored him. He then noticed that the bruises were on the man's face as well and appeared to have been punched several times, as if having been in a fist fight. The victim seemed to be young, probably mid twenties, had an athletic built and decent looks that was accompanied by clean cut hair. His clothes - a plain tee and slim jeans – were not removed; the top was just hiked up to show the missing torso, and the wallet was still in the back pocket. Ichigo checked it and noted that money was still in it. Money was clearly not the motive. Well, who the hell would cut a hole in someone just for money in the first place? The orange haired man's eyes studied the body carefully and immediately noticed something on the victim's lower back by the gaping hole.

"Saw it?" Urahara asked from behind him. Ichigo nodded and inched closer. It was the number six, carved deep into the flesh. It was most likely done with the murder weapon. "That's his signature."

"Okay…" Ichigo breathed. "Has his organs been found?"

"No. I suspect the killer either dumped it somewhere far away or the more usual case, he brought it back with him as a trophy," Urahara told him. Ichigo folded his arms and stared at the body, feeling slightly sick again.

"From the bruises, the guy probably got bashed up and when he was down, the killer went for the finisher. Then he did his… thing," Ichigo uncomfortably shifted as he glanced at the gaping hole in the torso. "Brought the body out here, since it's obviously constructed from the way the victim is lying down and there's not much blood here. "

"Good," Urhara smiled. "Anything else?"

"Looks like the whole thing's got its own symbolism – the open eyes, the slash to the neck, the hole…" Ichigo muttered more to himself. "…And this is definitely not the first time he's done this." Urahara nodded.

"It isn't," the Captain said. "This is his fourth, though it's highly likely that the first body found wasn't the real first either."

"What? You mean there's a serial killer on the loose all this while?" Ichigo asked him in disbelief. "How come I didn't know about this?"

"I'll let Abarai-san explain that," Urahara said tiredly as he nodded his head to someone behind Ichigo before going off to talk to a CSI.

"Oi, Ichigo!" Ichigo turned. A bright red haired man with shades on his forehead ducked under the tape and walked towards him.

"Hey Renji, what brings you here?" Ichigo asked after a simple nod of greeting.

"I'm on this case too," Renji replied as he peeked over Ichigo's shoulder and grimaced at the glimpse of the body he caught.

"All the way from the other side of town?"

"Yeah, well, the killer apparently has either killed or dumped bodies all over Karakura, so the whole town is involved," Renji told him. "I've been sent here by Kuchiki-taichou to assist your station."

"Byakuya? Why?" Ichigo asked dumbly. His sleepiness was making him ask questions rather than think.

"Your station's gonna be the headquarters for the homicide team which is gonna attend to this case," Renji said. "Jeez, man, you need more sleep."

"I know," Ichigo yawned. "Though having seen the victim woke me up a bit." Renji stepped by Ichigo and took a peek under the covers. He gave the same reaction as Ichigo did earlier but managed to recover from it faster than he did.

"…Yep, exactly like the other victims," Renji sighed and rubbed his hand all over his face tiredly.

"Right, how come I've never heard of this serial killer again?" Ichigo asked after remembering the unanswered question that was initially directed to his captain. He looked over to Urahara who was still talking to some CSIs.

"You were busy with your own case, and we just found out about this guy recently. We found his first victim half a year ago," Renji told him. "Then other precincts found more bodies with the same signature, and they seem to have been laid out in the open for people to find. All of us think he's now trying to get attention. Officers' been calling him the 'Rokuban (number six) killer'."

"Well it's pretty obvious where that name came from," Ichigo responded.

"I'll go report to Urahara-san first, you go do your stuff," Renji said and patted him on the shoulder before leaving. Ichigo nodded and began to look around, studying the environment and then observing the small crowd that had dissipated slightly. That was when he noticed someone standing one block away from the crime scene staring intently at him. The man was just standing there, leaning against a sign post and though Ichigo could hardly see him, he thought the man had a rather arrogant and smug air around him, from what Ichigo could see from his body language. Ichigo squinted and tried to get a good look at the man and from where Ichigo was, the man appeared to be tall and rather built, but Ichigo couldn't catch any distinctive features. The man was too far away and the darkness of the night and dim light posts didn't help. Before Ichigo could move to take a closer look, the man turned and left.

"Kurosaki-san!" Urahara called him, with Renji standing by him. Ichigo's head snapped back to look at him with an annoyed expression. "What are you doing?"

"No… nothing," Ichigo said and went back to where his boss was.

"Well, Abarai-san here will pass you some files on the previous victims, so get back to the station and get to it, ASAP. I'm counting on you Kurosaki-san, Abarai-san!" Urahara patted him on his shoulder and walked off. He turned slightly as he walked, to add, "Oh, and there should be some other detectives coming in to aid in the investigation!"

"And where are you going?" Ichigo asked.

"Sleep!"

-xxxxxxxxxxxxx-

Ichigo snapped his head up when he heard a loud banging noise and squinted his eyes as he tried to clear his vision. He looked around and remembered where he was. He had apparently dozed off on his desk that was covered in paper work and case files. It had only been 5 hours since he woke up to get to the crime scene but yet it felt like 5 days have gone. As he recollected his memory, four figures stood in front of his desk and Ichigo rubbed his eyes. One was a bald man with a scowl; an effeminate looking man with short straight hair; and a small woman with short hair and large dark eyes.

"Ikkaku, Yumichika… and… Rukia?" Ichigo asked drowsily. He still wasn't sure whether he was dreaming.

"Wake up, Ichigo!" Rukia said and slammed her hand onto the top of Ichigo's desk, causing the orange haired to jolt up and blink himself awake. "We're here to aid in the investigation of the 'Rokuban Killer'."

Ichigo blinked. Urahara had told him about a bunch of detectives coming in for the investigation, but didn't expect this bunch. Despite being detectives, they were a rowdy bunch and always seemed so carefree. They headed towards Renji's desk which was a few seats away and already making a lot of noise as they woke their colleague up. But Ichigo knew they were skilled in their field. They were sent by the captains from all over Karakura's police branches, after all. Kuchiki Rukia – sister of Renji's captain Kuchiki Byakuya, and a detective under Captain Ukitake Jyuushirou's precinct; and Ikkaku Madarame and Ayasegawa Yumichika - the strange but very capable duo of brute force under the notorious Captain Zaraki Kenpachi. Ichigo had known Renji and Rukia since they were in the police academy, and had met Ikkaku and Yumichika a bit later at a gathering for the whole police force. They were all pretty tight, and having them all gathered here for an investigation would certainly make it interesting. It would be the first, but Ichigo was looking forward to taking this unidentified subject of a serial killer down together.

"Ah, right, Urahara-san told me… Lemme wash my face first, you guys can ask Renji for a debrief of this morning's victim. I think he's also sleeping at his desk," Ichigo told them.

Ichigo entered the empty restroom and quickly turned the tap on. He splashed some water on his face and rested his palms on the sides of the sink. He avoided looking at his reflection in the mirror in front of him, but he felt the pull to just look. There, in his reflection, he saw it. The darker side of himself. A side he hated, and even feared. Seeing the victim last night must have stirred him up, and going through descriptions and photos of the old murder cases was affecting him again. Ichigo was pretty used to this – or so he thought. He had been aware of this side since young, but he knew how to control it. He knew what was right and wrong. He knew he wasn't meant to submit to this darker side of himself.

His job required him to think like a killer. Thinking like a killer was easy – almost everyone would have thought about killing or acting violently towards another living thing at least once in their lifetime, no matter how much they deny it. But what scared Ichigo the most was that sometimes he felt the pull of that desire. With that tiny little voice in the back of his head, whispering things to him; to fight, to hurt, to kill – every time he looked at the victims and read the autopsy reports by the coroner. What was it like to be the one taking the victim's life? The thrill of killing someone, the high the killers get when they perform such atrocities. He had wondered about them ever since young. But he wasn't a killer. Ichigo had tried to convince himself that he wasn't capable of such a thing. Such a blatant lie would never sink in, though. And the little voice in his head laughed and agreed.

Admittedly Ichigo felt a little nervous being sent to take on this case. Excited, yes, but he feared he would get too excited. He had felt the excitement when he was at the crime scene then – that desire to be in the killer's shoes had risen as he looked at the gaping hole in the victim's stomach. How did it feel to dig that knife into the victim's flesh, cut his throat and see the life and blood drain out of his body?

Ichigo shuddered at his own thoughts and willed them away. He turned away from his reflection and exited the restroom to get back to work.

"Ichigo, you okay? You don't look too good," Rukia asked when Ichigo reached the meeting table that the group had moved to. Ichigo shook his head and sipped on the coffee that he had grabbed before coming to the table.

"The victims making ya sick?" Ikkaku asked as he looked through the crime scene photos.

"Disgusting," Yumichika chipped in with great distaste.

"It really was," Renji answered. "But anyway, Ichigo, I've told them very briefly what we know so far. Evidence has been sent to forensics, body's with the coroner, and now we're just waiting for Urahara to be here and give us another brief for the investigation."

"But didn't he go back home to sleep?"

"You think he can when he's in charge of the team investigating this serial killer?" Renji replied and Ichigo kept quiet when he saw his point.

And speak of the devil, the man himself entered the room just as Renji ended his sentence. The man looked a little more refreshed but hadn't shaved the stubble off, so he still looked as messy. He had a pile of papers with him, which he set onto the table by the computer with a heavy thump. Urahara Kisuke was a genius, and also his personal mentor since the man was closely acquainted with his father. He had heard that the man was quite the legend in Karakura's police force. It was an honor for Ichigo to be directly under him, he guessed, but sometimes he found the man so eccentric and playful he wondered whether the people who called Urahara a legend were bullshitting him. But Ichigo had seen the genius at work, so he couldn't really deny it either.

"Ahh seems like you guys are all ready, should we start?" Urahara began with his usual sing-song voice. He started anyway without needing an answer. "Right. Let me start with a welcome to you guys. All of you were picked by captains all over Karakura and even screened by Yamamoto-soutaichou to lead this case. Just so you know, this is our very first serial killer case in a very long time. This may be your first exposure to serial cases, but just like every other case, it's a race against time to track him down before he can get another victim. We will still get a lot of help from the other captains and detectives, so do not get excited, reckless or too involved in it, just because it is a big case. Once you get too excited, you will break down, and I do not need a broken detective on the case. Understood?"

Everyone agreed silently. Ichigo noticed that Urahara was staring at him as he mentioned the warnings but ignored it. The captain started his presentation slides on the computer which popped up on the projector screen.

"So, we officially found Mr. Number 6's first victim half a year ago. And from then on, we found 2 others with yesterday being another one, which makes the total number of victims as four. From the investigation on the previous cases, we've already established an obvious pattern from the killer - his M.O. and when his victims are to be found." Urahara showed the team a list of dates on when the victims were found. "Lookie here, our suspect really likes the number six," Urahara pointed out. "He doesn't kill his victims on any date with the number 6, but he places them for the public to find on any date with the number 6. So far none of them are killed six days after the other, usually a few weeks after but in a worst case scenario… He just might."

Urahara clicked on the mouse and photos of the victims popped up. Most of them were focused on the slash to the neck, the gaping hole and the carved 6 on the flesh of the victim. The whole team grew uncomfortable, with Yumichika and Rukia looking like they were going to puke.

"The killer's signature," Urahara simply said. "All four victims' C.O.D were the slitting of the throat, and all of them were mutilated this way after their death – their stomach carved out, along with the intestines. And of course, the slanted number 6 by the side. The organs were never found so it's highly likely they were kept as trophies."

Urahara clicked on the mouse again and more photos popped up, this time, on the bruises that were all over the victims' bodies. "Now, the modus operandi of Mr. 6 here is pretty unusual," Urahara began.

"Are those bruises… pre-mortem? And from some kind of fight?" Rukia inquired as she studied the photos on the projector screen.

"That's right, Kuchiki-san," Urahara replied with a smile. "Apparently these bruises were from a physical fight just before they died. All victims are physically fit men trained in hand to hand combat. Some even have weapons on them. They were perfectly capable of defending themselves…"

"And yet they still fall prey to the predator," Ichigo muttered. Everyone looked at him, even Urahara, who just raised an eyebrow with interest.

"…Moving on," Urahara continued but his eyes didn't leave Ichigo. "This killer apparently seems to be seeking a thrill in getting victims who can actually fight back. He separates the victims from the crowd – which are usually from the bars that he apparently frequents – starts a physical fight with them before finally killing them by slashing their throat."

"Then he starts that sick Jack the Ripper crap," Ikkaku added.

"Yes, something like Jack the Ripper I suppose," Urahara said. "We are unsure whether these victims are the only victims that our killer has. It's highly unlikely, since these victims were moved into very obvious areas where they are bound to be found. If he does have other victims, we probably won't find it because he doesn't want us to find it. We've already had a hard time looking for the original crime scenes as well, which is why so far we don't have many clues to go by."

Rukia raised her hand. "Yes, Kuchiki-san?"

"So are these killings motivated by a sexual fetish of some sort?"Rukia asked. Like a studious student, she was actually taking down notes as the briefing went on. That was probably why she was one of the better detectives.

"Probably," Urahara became pensive. "We found no signs of sexual activity, not even violation of the privates or traces of semen but then again… Some men experience sexual pleasure in the act of violence itself." Rukia nodded and jotted it down on her notebook. Ichigo pondered on that strange fact while Rukia asked another question. "Do we have a profile on him yet?"

"I'm getting to it," Urahara smiled. He clicked on the mouse again and the projector gave a list on the profile information gathered so far. "To summarize it, the No. 6 Killer is a process-focused serial killer with a thrill seeking drive. His murder weapon appears to be the same throughout – a military combat knife, and though we have taken into consideration that he possibly has military experience, we also have to consider that he may have acquired the knife elsewhere. We still have much more to cover before we can get a complete profile and that job is handed to you guys." The team shifted in their seat. "Well, any questions?"

This time Ichigo raised his hand. "Kurosaki-san?"

"I read in one of the reports for the previous victims that there was someone with blue hair hanging around with the victim," Ichigo said. "And there was another mention of blue hair with another victim."

"Oh?" Urahara looked sincerely surprised by that.

"But there's the possibility that he's just a regular of the bars. And there's a lot of people dying their hair," Yumichika said skeptically.

"Then we can perhaps check out a list of anyone with dyed hair? Natural blue hair even?" Ichigo asked.

"It's just blue hair, Ichigo," Renji told him. "Just like you with orange and mine with red." Ichigo took slight offence in that comment, not about the hair, but the implication that his point was not important. But well, it was true. There was no basis that it was the same man with blue hair. But Ichigo just had the feeling that there was something about it. It isn't everyday that you see someone with blue hair.

"Then I'll use my own time to search it," Ichigo said stubbornly.

"Alright then, but don't forget to keep me posted, Kurosaki-san, you're pretty reckless when it comes to catching the suspects once you know their identities," Urahara reminded. Ichigo nodded with tightly pressed lips. "Right, now we can start the investigation proper. Do your thing you guys, you don't need me to tell you the routine work you do for every case. Kuchiki-san and Ayasegawa-san, you're in charge of looking through missing persons and interviewing. Kurosaki-san, Ikkaku-san and Abarai-san, keep up the paperwork and check through the list of ex-convicts. Don't forget to contact the forensic examiners like Ishida-san for the evidence reports. Just remember to keep each other and especially me, informed on what you have found out so that we can tie things together. Understood?"

"Yes, sir," the team replied.

"Alright, dismissed~" Urahara said a little bit too cheerfully. As the team stood up, Urahara added, "Oh, Kurosaki-san? You'll have to help me in getting a psychological profile from psychiatrists." Ichigo groaned but nodded. He never liked psychiatrists. He'd had a bad experience with them. Trying not to think about it, the orange-haired man stretched and wanted to go for a refill of coffee when an officer entered the room.

"Excuse me detectives… but I think we found the organs of last night's victim. "And he's left a message," the officer announced. Ichigo felt a chill run up his spine at the mention of contact from the killer. The voice in his head snickered, and in the rare event, spoke to him.

Let's go see what Mr. Number Six has to say, aibou.

xxxxxxxxxxxxxx End of chapter 1 xxxxxxxxxxxxxx

I had a lot of fun researching materials for this fanfic, though I have to say that not all information may be correct. I've always been interested in this topic, and Grimmjow suits the profile. Arrogant, sadistic, and gets a thrill from violence. Well that's what I see in him anyway. Hope all the information didn't bore you… well if it did I don't think you'd be reading this part anyways, so thank you so very much for reading all the way through! Please leave a review/comment! I want to know what you think of this, content-wise at least, because I know the writing isn't as good as I wanted it to be ^^;

Edit: Gurrr FF(dot)net and their goddamned messing up of line breaks...