Antimatter. A mere 0.1 gram can put off as much energy as an atomic bomb can. Yanagisawa's research has enabled continuous generation by splicing the antimatter particle acceleration cycle into a living being. Legendary assassin the Reaper spent his days going under those experiments. The antimatter energy that had begun circulating within his body  had replaced his body tissue with thought and flexible structures.

Koro-sensei was seen unconscious as his fingers elongated and wriggled back and forth.

Yanagisawa called them 'tentacles and fearing them, reinforced the restraint table...

Before, Koro-sensei's arms had no restraints on them but now, they were encased completely as he underwent the experiments.

...and left the dangerous monitoring to Yukimura Aguri. And so she knew. She knew that the Reaper did not know his real name or his birthday. She also knew that his kind words and smiles were studies--as means to kill.

Koro-sensei was seen laughing as he conversed with Aguri.

And he knew. He knew that there was no love between Aguri and her fiancee, Yanagisawa, and that she had a younger sister, a keen actor, whom she was very proud of.

It had already been nearly a year since the two have met. Along the way, the room had become a space for them to chat.
*
" Oh right! " Aguri exclaimed, standing from her seat and getting Koro-sensei's attention from his reading, " Look at the undershirt I bought today! "

" You never learn do you? There's no sense dragging down womankind with your tasteless fashion. " Koro-sensei chuckled as he stood up.

" Ta-da! An ogre-patterned tube top! " Aguri smiled as she unbuttoned her lab coat to show her tribal-coloured tube top with red and blue ogre faces at the top rim, " It's a bit tight but stylish, isn't it? "

Koro-sensei stared at her breasts that were on display in silence before a perverted smile spread across his face and blood dripped from his nose. Aguri stood, uncomfortable and sweatdropped at Koro-sensei's stance, not knowing what he was thinking.

" It's weird, isn't it? " Aguri asked shyly, " I just thought it was cute and... "

" N-No! This isn't what it looks like! " Koro-sensei stammered out as he turned away and covered his nose.

'Could the experiments be doing this?' he wondered as his fingers unknowingly started to become tentacles again.

" You have some honest tentacles there it seems. " Aguri giggled.

" Huh? "

" The way your hands can take on any shape, they might just reflect who you yourself would like to be. " Aguri explained.

" Me? "

" Had you been born into a peaceful world, you would have been smart but slightly perverted, a tad doofy, petty, headstrong and able to pull off an honest-to-goodness kind smile. " Aguri elaborated.
*
" Akari, I found some free time tonight. Want to grab dinner with me? " Aguri asked cheerfully.

" Eh, you sound so awfully happy right now. Who's the new guy? " Akari teased from the other line of the phone.

" Huh?! I-I'm engaged! " Aguri defended.

" Who cares? You should just cut that two-faced tyrant loose already. " Akari said nonchalantly as she sat in a cafe.

" Listen here-- "

" But sure. I can't wait to hear all about this new guy of yours. " Akari snickered.

" So we're on? "

" Mm! Your treat! "

" Geez... "
*
" A present? " Koro-sensei asked in disbelief.

" Hai, you said your neck was getting cold so I got you a scarf. " Aguri nodded, " This covers a good-sized area and is snazzy too! "

" T-Thanks. " Koro-sensei said as eye twitch constantly and his lips were twisted, showing his disgust at the design.

" I can see you don't like it. " Aguri mumbled.

" No, its just---why a present so suddenly? " Koro-sensie questioned.

" Today marks a year since I've first met you. If you don't know your birthday, why not make it today? " Aguri suggested, " You've lent me your ear and gave me so much advice. As my thanks for meeting you, let me give you a birthday. "

" I'll take it. " Koro-sensei nodded with a small smile.

" Wonderful! " Aguri sighed as she placed a hand on the wall separating them, " But I guess I can't give you this. Not with this wall around and...Yanagisawa wants me to quit my teaching job and work full-time here. The students in my last E class...I never did manage to put a spark in their eyes. I'm still too green for these new kids and yet... "

" But my students are all good kids! All so unique, earnest and genuine! " Aguri raised her voice slightly, " That's why I want that job, to help them. Because I like them all...Reaper-san, I want to touch you. You've been my rock. I want you to give me strength to hang on until the end of the year. "

Slowly, Koro-sensei placed his own hand on the wall, at the same spot where Aguri's hand was, eliciting a gasp from her as she looked up and saw him smiling at her encouragingly.

Before he knew it, his smile was no longer false and was the real thing.

Strings from him passed through the small holes of the wall and produced a hand that touched Aguri's cheek, holding her lovingly. Koro-sensei leaned his head against the wall.

" It'll all be ok. You can do it. " Koro-sensei said confidently as Aguri leaned on the wall as well.

" Hai... "

The first time they touched was three hours before the crescent moon came to be.
*
" The moon?! " Yanagisawa shrieked.

" Yes! 70% has been destroyed! A lab rat on the lunar surface experienced a discharge of antimatter energy! " his subordinate confirmed.

" So cell division exceeded natural limits, huh? " Yanagisawa muttered, " Calculate the day this same phenomenon can occur in a human! " he ordered.

" Yes! " his subordinated sweated nervously as he furiously typed away on his computer with is superior breathing down his neck, " March 13 of next year! "

" That's the day he and the entire world will be destroyed. " Yanagisawa hissed as Aguri gasped and hid herself behind a wall, outside the room Yanagisawa was in.

" What should we do, sir? "

" Isn't it obvious? We will put him down. Should be easy enough if we can stop his heart. " Yanagisawa barked out orders, " Notify our U.S. HQ at once! "

Aguri had ran off by then.
*
" Doomed to a cursed death. I had that coming. " Koro-sensei remarked, not panicking.

" Don't give up just yet! There may be a way to save-- " Aguri began but was cut off.

" But since I have this power and all, " Koro-sensei raised a fist and looked down on it, " this is farewell, Aguri. "

He turned behind and declared, " I'm leaving this place. A little earlier than planned but this much power is enough. Enough for a place like this. "

Tentacles sprouted from his body, tearing parts of his clothing with his hair elongating as well.

" No! No more evil! After all the time we-- " Aguri protested.

" You're going to stop me? " Koro-sensei asked.

" Hai! " Aguri answered without hesitation.

" How? With those arms of yours? That brain? " Koro-sensei mocked as he placed hand on the wall.

" Huh? "

" Unless your abilities transcend mine, you can't stop or save me. " a crack appeared on the wall, " You're not even worth taking hostage. "

Another crack.

" Now leave before you die a pointless death. " Crack.

Aguri stood in front of the cracked wall in shock for a few moments before she regained her bearings and turned around, headed to the door.

" It's Yukimura. Please open Door 1. " she uttered.

Koro-sensei heard the opening and closing of the door swiftly as the cracked wall didn't allow him to see the other side.

" Now, to try out the powers I've gained by putting up with the torture! " Koro-sensei said excitedly and soon, his body swirled around and the CCTV footage of the room was cut off.

" What's wrong with the security system?! " Yanagisawa asked angrily as bells rang in the facility.

" A-A powerful mucus is jamming them so they aren't working at this moment! " his subordinated answered.

" Thanks, Yanagisawa. " Koro-sensei said, causing Yanagisawa to look towards the only CCTV camera working at the moment to see Koro-sensei's hair longer than it was and pure white, " Thanks to you, I have this invincible body now--with some of my guidance as well. "

The camera was then broken with a tentacle causing Yanagisawa to slam a fist on the panel.

" Is he saying he has been manipulating me and the experiment this entire time?! " he snapped.

" Kotaro-san! " Aguri ran in, " You have to help him! "

" You bitch! " he roared and shoved her to the ground and began kicking her in the stomach, shocking his subordinates and colleagues, " Fawning over any man that comes along? Is that the gratitude I get from you?! Who do you think you are?! You and him?! "

" Dammit! Gather the guards together and intercept him! " he barked out.
*
Two rows of armed, black-clad guards stood in the middle of a hallway with Yanagisawa in the middle with his arms crossed against his chest and a scowl present.

'Don't get ahead of yourself, you guinea pig. And don't think we were always about experience either' Yanagisawa gritted his teeth as a wall a few metres in front of them was destroyed into pieces.

Emerging from the hole was Koro-sensei with pure white hair reaching the ground, tentacles all over his body wiggling about and his clothes were torn, showing his chest.

" Shoot! " Yanagisawa commanded as BBs were sent flying towards Koro-sensei's direction.

" If all you're after is a ruptured aorta... " Koro-sensei began as he killed two of the guards by flicking a bullet at them that pierced them at vital parts of their body, " ...a grain of salt will do. "

Yanagisawa stared in horror as more guards were taken out.

" I could have killed the likes of you any time. " Koro-sensei said as he stepped forward but a thin green pole-like object shot out from a wall and pierced Koro-sensei square in the torso.

'Tentacle mines! A byproduct of antimatter organisms...attach sensors to them and the become weapons attacking at subsonic speeds ; transplanted in humans, they grant superhuman battle powers!' Yanagisawa smirked in glee as more of these tentacle mines stabbed Koro-sensei but his triumph was short-lived as Koro-sensei rose form the ground wile the tentacles mines were no longer useful and wiggled about before going motionless after a single attack.

" That isn't enough to kill me! " Koro-sensei laughed manically as his left eye glowed red.

" K-Kill him! Surround him! Exterminate him! " Yanagisawa ordered messily in fear as more guards ran towards Koro-sensei's direction.

Koro-sensei continued to laugh as he killed the guards swiftly with his tentacles and began to move at Mach speed 20.

" Drop the reinforced acrylic! " Yanagisawa shouted and a wall similar to the one in Koro-sensei's room dropped from the ceiling, cutting off the path only for Koro-sensei to fling a syringe towards the wall fast enough for it to gain enough energy and break the wall, going through it and stabbing Yanagisawa in his left eye.

He screamed as blood spurted out while Koro-sensei continued his rampage with no signs of stopping.
*
The facility was in shambles, a wreck. Aguri slowly looked up form where she was lightly buried by rubbled, not harming her. She could see Koro-sensei's silhouette with his tentacles going wild in the air. Aguri slowly approached him, stumbling here and there.

" I'll die in a year regardless. It doesn't matter if I die here or not. I don't mind dying with the earth either. " Koro-sensei mumbled as he stood up, ready to leave with his intentions but was stopped in his tracks as Aguri wrapped her arms around his torso form behind with a sound 'no' coming from her.

'If you go that way...there's not coming back!' she thought desperately as she held him.

She had seen everything. Seen everything and was curious about it. But her being there, seeing me...that's something I had not seen.

Koro-sensei looked one this shoulder at her, his eyes widening.

At that moment, a tentacle mine had detected him and shot at him...only to pierce Aguri instead.

" Aguri! " he exclaimed as he caught her before she could hit the rocky ground.

" Now I've done it. Didn't think a trap would slither out like that... " Aguri chuckled weakly.

" Why? " Koro-sensei demanded.

" I knew...my voice wouldn't be enough...to stop you... " Aguri smiled.

'If I had been 0.1 second faster, I could have protected her. If I'd practice how to heal with my tentacles, I could have saved her...why? I had plenty of time...' Koro-sensei thought, distraught, 'Why didn't I use my deadly, destructive strength to help someone? Why Why?!'

" I may as well have killed you myself... "

" Of course you didn't... " Aguri assured him, " I just did what I...wanted and...I don't mind...being killed...for you...That's just how important...you are to me...One day, you too will meet someone like that... "

" If you were the one to kill me, I'd have no regrets, but to think there would be someone like you out there-- " Koro-sensei halted in mid-sentence as Aguri coughed out blood.

" In this year you have left, if you would give your time...to teach those children... " Aguri requested, " ...they're just like you...wandering in the darkness. If you look at them head-on, I'm sure... "

" What splendid tentacles... " Aguri praised as she held onto a tentacle, "...With hands like these, I'm sure you'll be a great teacher... "

That was the last thing she could utter out as she placed a hand on his cheek before going limp, her hand sliding off of his cheek.

He slowly laid her body on the ground, brushing her hair gently as he held a necktie in his tentacle-like hand, almost completely transformed.

At long last he realised, her faults were part of her charm.

He clutched the necktie tightly in his grasp.

'I'll use the time have left to be a teacher' Koro-sensei thought as his tentacles brought pen and paper to him, writing out a message, 'To keep looking, with my eyes at the students you've been watching'

He placed a tentacle at her wound, 'I won't let go of your students no matter what'

Akari, at that moment, arrived at the scene to see the silhouette of the tentacled monster standing up and leaving in the blink of an eye.

'The tentacles at that moment asked me what I wanted to be. I wanted to be weak. To be riddled with weaknesses, easy to talk to...To be able to perceive the weak, protect them guide them...To be that kind of creature...that kind of person'

Koro-sensei crashed at the mountain where the E class campus was, his transformation complete as he now had yellow skin and his tentacles' formation stable.

'Sometimes I'll be wrong. Sometimes my cold-hearted true face may even show. But I'll give it my all. I'll aim for her own goal my way, the way I do best'

Koro-sensei's new body emerged from the ground, complete with clothing and the necktie he received from Aguri as he overlooked the town from the mountain top.
.

.

.
" That's my story. " Koro-sensei concluded, " The one who taught me to be a teacher was Yukimura Aguri. To truly look at the people before you, not to judge them solely based on weaknesses... "

Kayano began to sob.

" I learned the fundamentals of being a teacher from her. I added my own knowledge and experience and prepared to face you all. I would use my abilities to the fullest to give you the gift of the best growth and development. " Koro-sensei continued, " But how best to do that? I thought long and hard and finally landed on the assassination classroom where I'd use what remained of my life. "

The students had then realised the challenge they had brought upon themselves as they recalled all the times they spent with Koro-sensei ; especially the fun times.

'Do we have to kill this teacher of ours?' was what ran through the minds of he students.

Karasuma and Irina both turned away with uncertain looks of theirs as well.

" Say, Karasuma? Do you really know what it means to kill? " Irina's question rang out.
*
It's now January 6, into the new year. The number of students plotting assassinations during winter break was precisely zero.

" The third term is upon us now, class! Let's study hard and kill hard this year as well! " Koro-sensei announced to the gloomy class as Karasuma and Irina too were present inside at the doorway.
*
" You must have known this would have happen. " Karasuma spoke up a he and Koro-sensei left the classroom for Irina to take over, " That they'd be like this. Especially now that you've placed heavy burden on them---can you really carry out your duties as a teacher? "

" If I weren't prepared to be flexible if the situation calls for it, I wouldn't have become a teacher in the first place. " Koro-sensei replied simply.

In the class...

" The most foolish kill is to kill recklessly, out of emotion or greed. That's what animals do. " Irina lectured, " Next is to kill your feelings while you kill your target, giving up very much in exchange for a bounty. Like I did. "

She smiled at them, " You really need to think this through, kids, so you won't kill off the