A/N: Keira Marco's Rough trade prompt bit me just a lil' bit. So here we have just over a thousand words of Sentinel fusion.

Assassination Classroom The Sentinel Fusion

Summary: Guide Karma causes the Civil War out of pain and confusion after Sentinel Nagisa Bonded with Guide Kanyo.

Karma could barely concentrate on his work. The Sentinel was calling to him. His cool, welcoming presence distracted Karma from the worksheet in front of him. It was a distraction he did not welcome, nor did he understand. Nagisa was a Bonded Sentinel after all.

When Nagisa initiated the Bond with Kanyo, Karma had been there. He had felt it. He had taken pictures for God's sake! So why was the Sentinel still calling to him?

He was happy for Nagisa, for Kanyo. Yes, he wanted it to be him. He had fantasized that it would be him. Had dreamed that Nagisa would ask to bond with him and fill the Sentinel sized hole in his chest, but that was not what happened. And that was O.K.

Nagisa had picked Kanyo. Great! They deserved to be happy, and they'd make a good pair. Karma wanted them to be happy.

Didn't he? He wasn't secretly trying to sabotage their bond was he? What if he was? Then it would be Pair Bond Interference and that was not only illegal, but also immoral. And Karma was not going to be a Bond Breaker.

Karma viciously tamped down on his Guide gifts. Reinforcing his shields and locking them tight. He focused all his concentration on the worksheet in front of him. He was so focused, he didn't see Nagisa jerk and look back at him with a confused look. Seeing Karma at work, Nagisa shrugged and returned to his own paper.

When Nagisa told the class he wanted to save Korosensei, Karma felt shock ripple through the whole class. Normally Karma could brush off the emotions of his classmates, but the singular emotion they produced fused into one. The intensity shattered Karma's shields. From that moment, Karma was compromised.

Later, the redhead would look back and pinpoint this as the exact moment when he lost all control. Later, he would recognize that he started to influence the emotions of those around him. Later he would apologize to Nakamura, to Teraska, and to the others for taking their control from them, and they would forgive him. But in the moment Karma knew none of this.

Karma just reacted.

He lashed out at Nagisa. First verbally, with nasty words he knew would hurt his long time friend. Then Nagisa argued back, and Karma changed his tactics. He pushed Nagisa. Then he pushed him again, but Nagisa fought back with a choke hold that no one saw coming. When did he even learn it? No matter, Karma was stronger and overpowered the hold.

The other students were quick to separate them before the fight could escalate.

Suddenly Korosensei appeared from nowhere. He devised a way they all could settle there differences, which was ridiculous. The fight had been about killing him! But then the lines were drawn and sides chosen. Karma quickly devised a plan on the best way to take out the blue team.

The battle began with a bang. Karma made sure the most deadly blue team members were taken out first. The fighting continued until the only two remaining were Nagisa and Karma. Finally they would finish this. A small part of Karma whispered, maybe this would stop the Sentinel from calling out to him once and for all. That same small part mourned the upcoming loss of his friend, but Karma saw no way they could come out of this with their relationship intact.

Karma and Nagisa faced off as their classmates gathered down close to watch. He could hear them murmuring to themselves, but had no time to pay attention. It was time to attack. This time no one would be stopping their fight.

Karma lunged with a snarl. He blocked Nagisa's blows with one of his own, but knew to be wary. He may have the strength over the smaller boy, but Nagisa had speed, and his Sentinel Gifts. Gifts which could be both benefit and detriment in a fight. And there was no telling what other tricks Nagisa had learned.

The pair continued to exchange blows, but Nagisa just wasn't strong enough. Karma took all his hits and plowed right through. He knocked Nagisa back again and again.

The other students were talking on the sidelines excitedly. Karma could not hear what they were saying, but every once and a while Nagisa's head would twitch. Karma used Nagisa's distraction to kick Nagisa back once again.

Kanyo yelled something as Nagisa went down. Karma retrieved his blade from where it had landed after being knocked from his hand. He glanced at the students and saw Kanyo looking nervous next to Korosensei before looking away. It looked like the redhead finally had the upper hand, but then Nagisa pulled out one of his tricks, the Nekodamashi.

Karma barely managed to avoid it's full effects. He watched through a haze as Nagisa scrambled to his feet and lunged at Karma. The blue haired boy had his own knife in his hand and Karma focused on avoiding it, only to discover that Nagisa had already let go, and they were falling to the forest floor. Nagisa's arms tight around his neck in another choke hold.

As Karma fought to free himself the noises of the world began to fade and the trees took on a blue tint. They grew taller and closer together. Karma knew this place, had walked the paths here in meditation. This was the spirit plane.

Karma felt Nagisa's snake, a pit viper, coil around their ankles even as Nagisa clung tighter to Karma's neck. The cool scales caused the redhead to shiver, as did Nagisa's breath on his neck.

The viper hissed.

A growl answered. It was a low rumbling sound that Karma knew well. His spirit animal, a majestic tiger, stepped into view.

Karma's breath caught in his throat. How were they here? Why were they here? A sliver of hope began to rise up through the confusion in the redhead. There were few reasons a Sentinel and Guide would drag each other into the spirit world. The most common was Bonding.

But Nagisa was bonded to Kanyo, the voice in Karma's head reminded him. Despair washed through him, and his tiger made a mournful noise. Nagisa hissed with his viper in reaction, the arms around Karma's neck growing impossibly tighter.

Without warning, the snake lunged at the tiger. Karma clung to Nagisa with all his might as he felt Nagisa reach out for him, a gossamer thread of a bond forming between them. This was what the Guide in Karma wanted, what all Guides wanted. If Nagisa was offering, then Karma would not turn him down. He wanted Nagisa. And he surrendered.

Their spirits merged.

When Karma opened his eyes they were back on the mountain. The sun had moved across the sky and the boys were now shaded by the trees. Looking to the side, Karma could see that the rest of class 3-E had left. They must have returned to class when they realized the fight was over. Karma could feel Nagisa both physically resting against him, and through their new bond.

Karma shivered at the thought. Their new bond. It made no sense, he had seen Nagisa initiate a bond. Had felt it. Had taken pictures of it and teased Nagisa with them.

Nagisa sat up beside Karma, who followed him up.

"How." Karma asked. "I have pictures."

"Kanyo and I are incompatible." Nagisa said, looking away sadly.

It was like someone had punched Karma in the gut. Incompatible, incapable of bonding with a Sentinel or Guide. It was rare, but Karma had heard of it happening before.

"It gets worse." Nagisa continued. "The formula that Kanyo infected herself with feeds off the centers of the brain where Sentinel and Guide gifts are found. She will never bond."

Karma looked at Nagisa in horror, but the Sentinel wasn't done.

"The formula only works on Sentinels and Guides. Itona and Korosensei are in the same boat. The damage to Korosensei is irreparable, but Itona and Kanyo might be repairable. If we know the full extent of what happened to them."

"And for that we need Korosensei's help" Karma finished finally understanding why Nagisa had insisted on saving their Teacher. It wasn't about him. It was about their friends.

Nagisa smiled and Karma felt his pleasure across the bond.

"Will you help me?" He asked the redhead.

"Yes."