Disclaimer: Guilty Crown belongs to Tetsuro Araki, Production IG and Funimation. Attack on Titan (Shingeki no Kyojin) belongs to Hajime Isayama, Tetsuro Araki, Production IG and Funimation.

A/N: Spring break is almost there. Some of you readers are waiting for this moment, a crossover with everyone's current popular anime that hit the mainstream and Guilty Crown. Now I once heard someone thought of doing it when he did a GC x Code Geass fic before it didn't happen, so I'm taking over the plot bunny (It finally happen because up until today, someone has yet to do it). This is a one-shot though.

It's both animes have the same studio, Eren/Shu have the same japanese voice actor, same music composer, and are both dubbed by Funimation. Attack on Titan's success is beyond anything we imagine in the 2010s of anime; surpassing Guilty Crown, Puella Magi Madoka Magica, Hunter x Hunter (2011 series) and Sword Art Online, even Kill la Kill still can't catch up. It is what some people see it as the next king, this year we're going to have a live action film, while next year Season 2 is in the works. The manga I know will be done soon with somewhere of 4 volumes left before reaching the total of 20.

Anyway, enjoy!

"And just like that, everything changed. At that terrible moment, in our hearts, we knew… "home" was a pen… and humanity, cattle."

(Cue Guren no Yumiya - Linked Horizon)

A Titan's Heart

Fields and Forest/Universe: AoT-09

(Cue Attack on Titan - Reluctant Heroes)

This is the world that is part of outside the walls. These trios of colossal walls are presuming to be made 100 years ago by humanity to protect themselves from man-eating giants called, Titans. Aside from their name originated from Greek Mythology, no one knows where they come from other than mindlessly eat humans for sport.

Humanity resort to defend themselves with three military branches: the Garrison Walls that guard the walls and basic stock troops, the Survey Corp which scout the outside borders and fight the Titans, and the Military Police which they are bottled in the inner walls to guard the king. They want to exterminate the Titans by cutting through the nape of their necks as their sole weakness. They do this with the 3D Maneuver Gear, also known as the Omni-directional Mobility Gear.

But at the same time, the humans wonder where their origins come from. These secrets have yet to be told.

Today, the Survey Corp riding on horses are having a skirmish in finding and killing any Titans nearby. They are led by Commander Levi, in which the scouts consists of: Eren Yeager, Mikasa Ackerman, Armin Arlert, Jean Kirstein, Connie Springer, Sasha Blouse, and Krista Lenz.

As they scout through a forest, they saw a few numbers of lumbering Titans.

"Just what we needed." Jean scowled.

"Well, you know what the captain said." Armin concurred to his friend.

Levi then orders his younger comrades, "Alright team, let's clean up this scourge!"

With the commander's orders, the 104th Trainee Squad takes action as they use their gears to glide through the trees. Only Armin and Krista stay behind on their horses.

Sasha happily screams out as she and Connie team up to take down a Titan, the giant attempts to grab them, but the humans easily dodge as they slice through the fleshy neck to kill the Titan.

Mikasa and Jean use their skills to leap through the trees and slice down some of the Titans' necks. Mikasa remains in caution to protect her adopted brother, even though Eren can handle himself.

Likewise, Eren is backing up Commander Levi to help fight off the Titans. Eren uses his ferocity to cut through one Titan's neck, while evading another Titan's grasps. Levi nonverbally reminds him to stand on his guard.

Just as the scouts slay a few numbers of these monsters, more hordes of Titans are coming this way. The Scout Regiment are about to be outnumbered obviously, as they begin to regroup. Eren on the other hand, can't take it anymore as he gets off his horse and glares at the Titans.

"Eren!" Mikasa cried out in concern.

"Stand back Mikasa, I'll handle this." Eren replied to his adopted Oriental sister.

"Feh, this outta be good." Jean sarcastically quipped.

The scouts watch of seeing their trump card in their hands. Eren is about to bite his thumb as the Titans are coming closer.

(End Theme)

Before Eren does so, an unearthly beam suddenly hits to the ground out of nowhere. The surrounding aura of the beam backs off the Scout Regiment and the lumbering Titans much to their surprise.

"W-What is that light?" Krista muttered of feeling something inhuman.

As the light fades away, it reveals two figures standing there. One is a brunette-haired boy with a scarf and a black trench coat. The other is a beautiful girl with long artificial pink-hair and wearing a white dress.

The scouts are taking notice to the two strangers.

"Who are you?" Eren questioned the visitors he and his comrades have never heard.

The brown-haired stranger turns to Eren and the Survey Corp to respond, "Don't worry, I came to help."

(Cue Attack on Titan - EMA)

With that said, the stranger's right hand glows in revealing a black crown symbol. He places his hand on the pink-haired girl's body in grabbing something inside, pulling it out in revealing a longsword that is the size of a javelin. The stranger turns towards the Titans, as they begin to attack.

"What kind of power does he have?" Armin's eyes widened.

The pink-haired girl responds to the Caucasian blond-haired boy, "He simply just uses me."

The brown-haired boy then leaps in a supernatural feeling through the mass of Titans without fear, much to the scouts' intensive surprise. The giants attempt to grab the boy in their attempts to devour him to pieces, but the scarfed stranger evades their grasp as he lands in one of the Titan's shoulders to slice through its neck, killing one.

The boy then uses his sword to jump and easily beheads another Titan like butter, further impressing the Scout Regiment. Deciding that they no longer stand idly, Levi leads his team to help out the stranger.

Krista approaches the pink-haired girl, "Are you going to help out?"

Just then, an abnormal Titan appears behind the two much to Krista's shock. Before the frenzied giant reaches them, the pink-haired girl conjures some sort of crystal tendrils to ensnare the Abnormal Titan, and then she finishes for the crystals to engulf the Titan till it turns to dust.

"Yes..yes I am." The mysterious girl said to the surprised Krista.

Meanwhile, as the skirmish battle wages on, Eren Yeager appears beside the brown-haired boy. Both are standing in a large branch.

"Seriously, how did you do this?" Eren questioned the stranger about him having that void-like sword from the girl.

The brunette-haired boy turn towards Eren and respond, "Would you like to demonstrate?"

Eren feels unsure about it, "No, that's not what I meant."

"Don't worry, this won't take long." The young man reassured to the brave soldier.

Eren gulps about him playing the part of being the stranger's mere weapon, but slightly accepts to see if it's worth it. The boy then uses his right hand to grab something inside Eren and begin to utilize it.

Once he does so, the stranger then starts to glow as a lightning bolt zaps on him, making Eren taking cover as he glides to another set of branches.

As the smoke cleared, Eren and the Survey Corp are shock of what that young man does. With Eren's thing inside him, he has the ability to become some sort of, Titan Shifter!

"No way." Jean muttered. Levi glares at the man's Titan appearance on the other hand in suspicion.

The young man's Titan form looks similar to Eren's, except there are pale-teal green tron lines on his arms and legs, and has tendrils around his neck similar to an organic scarf. He then gives an earth-shaking roar like a Tyrannosaurus-rex. Eren's description is what it called, the Titan's Heart.

The stranger's Titan form rushes in delivering blows to the Titans. He swiftly charges at one Titan in headbutting it and then tears its head off. Titan!stranger beats down another Titan, while giving another giant a sky uppercut. The guest delivers a karate chop in chopping through the flesh armor of a Titan's neck.

The carnage the Survey Corp they witness becomes awestruck. After a few seconds of doubt, Eren begins to snap out of it and immediately decides to help. He bites his thumb so hard that he instantly feels the bolt of becoming his Titan form. Mikasa and Armin witness their sole hope coming from Eren, as the Rouge Titan gives an beastly roar before charging.

"Two Titan Shifters at the same time, what in the world are we living?" Armin pondered.

"I don't know, but this person is giving us the edge." Mikasa replied to her meek friend.

Titan!stranger senses that Titan!Eren appears to back him up. With both agreeing to team up, alongside the fact that this mysterious boy is 'using' Eren with responsibility, the Titan Shifters are punching through a flood of Titans without sweat. Most of the hungry abominations are no match for the two Titan fighters.

"Let's finish this, people!" Levi firmly ordered his comrades to help Eren and the stranger.

The older commander and the younger scouts are backing up the two Shifters with their blades cutting through Titan necks and also give them distraction so that Eren and the stranger can finish them off. The pink-haired girl also supports her allies by shooting crystals at the Titans to destroy them.

The skirmish battle goes on until when every Titan in this area is exterminated. It is a day to remember for humanity.

(End Theme)

Fields

In the aftermath of this skirmish battle, the Survey Corp have never felt expected to receive help form two guests. Just who are they? What power does that boy wielding these things coming people's hearts? Especially when using Eren that can make himself a Titan Shifter in turning the tide.

At the plain fields near Wall Rose, the couple is seen being questioned by Eren, Mikasa, Armin, Jean, Krista, Sasha, Connie, and Levi. Both Eren and that young man are back to normal from their Titan forms as the latter returns the 'thing' back inside Eren.

"We know why are standing here talking." Levi stated with his arms cross, "Though you two helped us from the Titans, we want to know about your identities."

The guilty couple takes notice at first from the stern commander's words.

After a few seconds, the brown-haired boy introduce himself alongside the pink-haired girl. "My name is Ouma Shu, and this is my lover, Yuzuriha Inori."

"It is nice meet you all." Inori politely bowed to the scouts.

"I see, the name is Eren Yeager." Eren introduces to himself while thanking Shu's assistance back then, "And the group I'm with are called the Survey Corp that we hunt to kill Titans."

"Interesting to say." Shu commented.

"Hmm, I take it that you two are from the outside world?" Armin wondered in theorizing the connection between Shu and Inori. He and some of the others are also curious if Shu and Inori are similar to the near-extinct Orientals.

"No, we just came from another world different from yours." Inori calmly answered.

"Likewise, me and Inori are briefly summoned to this place as some way to help out people from other dimensions." Shu stated and chuckles, "Well, we don't want to interfere too much, just simply guiding guests."

"There are other universes? Intriguing." Armin said in surprise upon learning it, as if knowing the world outside the walls is enough.

Connie then interjects, "And how did you do these 'things' like you did with Eren? That Titan form of yours is phenomenal!"

Shu sighs a bit in responding the bald boy's enthusiastic curiosity, he then answers, "They are called Voids. The hand I have inside is this Power of the Kings. It draws out people's essence and use them as weapons and other things as away to support me in battle. It ties something with friendship."

"Cool! I wonder what mine's look like?!" Sasha happily cried out.

"Are you so eager to try?" Shu asked the brown-haired ponytail girl.

Sasha nods by giving the 'uh-huh' expression. The scouts begin to observe more of this void power since the experience with Eren's void. Shu then uses his right hand to grab something from Sasha's body as she cries out. Her own void reveals to be a potato for the viewers to see.

"What the heck?! A potato?!" Sasha gasped.

"Haha! Isn't it obvious?" Connie laugh of knowing that is her favorite food.

"But that means I'm not that special!" Sasha sadly cried out.

"Relax Sasha, your doing fine just now." Connie cheered the energetic girl up. Shu then puts back Sasha's void to her body while she sighs to herself.

Next, Krista quietly decides to volunteer as the group watches Shu drawing out Krista's own void, it turns out to be a flute.

"Yours is pretty special despite being a beautiful instrument." Inori commented to Krista. "I believe you might play a big part at some point."

"Really, I just..?" Krista doubts about herself.

"You will find out someday." Inori reassured.

Shu then puts back Krista's void before he turns to the Survey Corp, "Anyone else for those that are under 18? Okay, that's part of the rules when I'm using its power."

The younger scouts begin to think amongst themselves in case.

"I bet Jean's void looks like a horse." Eren joked with the rest of his friends laugh at the compliment.

"What the hell is that suppose to mean?!" Jean angrily shouted at Eren.

Before they can further decide of getting acquainted with Shu and Inori, a white light suddenly appears in front of the group. Shu and Inori senses this familiar feeling as it begins to take the appearance of a young girl's spirit, kinda like how a white rabbit is formed. She has brunette hair kept in two red bows and brown eyes.

"Menjou Hare." Shu muttered of knowing an old deceased friend. Eren is mesmerized of seeing the innocent beauty within that girl.

"Shu, I'm glad to see that you and Inori's time here are going fine." Hare smiled of being as a heavenly messenger. "It's time we have to go soon."

"I understand." Shu replied to his former high school classmate.

Eren then interjects and said to Hare, "Your voice feels familiar. Is it someone named, Annie Leonhart, or is someone else for what is like a dream?"

Hare smiles and giggles at the Caucasian boy, "Don't worry about it, someday you'll find someone special."

"R-right!" Eren replied to the spirit before turning to Shu and Inori, "I guess you two are leaving, huh?"

"Yeah, we have other priorities to explore, but we're glad of assisting you and your friends." Shu said to his new friend.

"I'm glad my void paid off in slaying those Titans, Shu." Eren smiled at the foreigner.

Shu smiles back as both he and Eren shake hands as a sign of their friendship. "No problem, you helped me out as well."

"It's good to meet you, if only I like to know what my own void power is like. My feelings for Eren are strong." Mikasa stoically said.

"This we got to research more of what's going outside in general." Armin cried out of having some ideas.

"We'll make sure we support our world with dignity." Levi stated to Shu and Inori.

"Good luck with your journey, man." Jean casually said to them with Sasha, Connie, and Krista having the same response.

The time for the guilty couple alongside their angelic messenger is at hand for their leave.

"Bye." Inori simply said her farewells to the Scout Regiment.

With that said, a bright light from the clouds surrounds Shu and Inori with Hare's guidance, as the trio makes their departure from this dimension. The light then disappears.

As the brave Survey Corp watches the skies above them, they wonder about the laws of other worlds besides having their concerns on their own? Eren himself has his determination since he's gotten to know someone similar to himself, igniting his idealistic purpose for the world.

(Cue Utsukushiki Zankoku na Sekai - Yoko Hikasa)

A/N: It's done. Glad how it turned out, although I made it a little short instead of being long as some readers expect. I like having Shu as a Titan when using Eren's void, it is coincidental. Eren interacting with Hare's spirit references that Hare's Japanese voice actor does Annie Leonhart, I imagine them being a fan-couple.

Originally I was supposed to show Jean's void, but I don't know how to translate it well (could be something related to horses). Same goes for Connie, Mikasa (her void I describe is strong), and Armin.

Yes, Krista is mentioned as something special because for those that read the manga, she plays a much bigger role.

Either way, since it's a one-shot, some readers think I like to continue this, but I'd say no. It's fine as it is.