Chapter 1

"Do you have any idea what kind of a disappointment you are?!" Y/N's mother started with her daily dose of nagging her daughter. The Y/L/N family was not at all happy with their daughter studying at the end of the class of the infamous Kunugigaoka Junior High School, a prestigious private school renowned for being one of the top schools in all of Tokyo and has a high rate of successful students. But that wasn't all.

This school has something called 'E system' which serves as the lowest and worst class, based on their academics, behavior as well as extra curricular activities. This is used as a driving point for the 95% of students to strive academically so that they don't end up as that 5%. Needless to say, Y/N was a student of class 3-E, bullied and disrespected by the other sections just like the rest of her classmates.

Right now, her mother was scolding her for not being able to score better and escape the E system. This happened everyday, whenever she was with her parents. She locked herself up in her bedroom as soon as she came home, tired of getting the same words from her parents. Did she study? Yes, she tried but the only subjects that she was good at were the language papers. It's something that she was capable of doing since she spent a lot of time alone, reading in her room. Reading storybooks and writing short stories on some online contests was what she did to escape from the hell she was stuck in.

It wasn't just the fact that her parents reminded her how much of a loser she was everyday, but nowadays they started to nitpick on her appearance as well. Most of the times they compared Y/N with their relatives or some friend's daughter - how she was gaining weight and wasn't even near the ideal figure that she should have, since she didn't have the brains. And she was as a matter of fact, when she was under so much stress and anxiety.

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It started with two big things that happened in the third year. One minute it was fine, but then out of nowhere it turned into crescent - about 70% of the moon destroyed. It was all over the news, as soon as NASA confirmed.

And the second thing was the new homeroom teacher of class 3-E. And this was his words exactly - "So, I'm the one who blew up the moon. Next year I intend to do the same with planet earth. But nevermind that now, I'm gonna be your new teacher. Isn't that exciting!" It was a strong first impression. Besides, he looked nothing like human, and had a somewhat similar look as that of an yellow octopus.

There were three people standing alongside him. One of them was dressed professionally in a black business suit with a white shirt and a black tie. He had spiky black hair and eyebrows, and piercing dark eyes. He cleared his throat and introduced himself.

"I am Tadaomi Karasuma from the Ministry of Defense," he started stuttering, being careful with his choice of words, "What uh...what I'm about to tell you is called classified. Oh hell, I'll just come right out with it. I'm gonna need you to kill this thing for the sake of mankind."

Takuya asked a question that was running through everyone's mind, "Excuse me, uh- no offence but is this a joke cause if that's the alien who blew up the moon then-"

"I AM AN EARTH BRED, THANK YOU!" the new teacher fussed like a child.

"I am not in liberty to discuss the details. I'll just say he's telling the truth. His threat is all too real. As of this coming March, he will obliterate the Earth. Apart from you, the only people who know about this are world leaders. If a word of this leaks out to the public, we will have a widesperead panic in our hands. He must be terminated soon and with extreme prejudice," Karasuma took out a knife and attacked the teacher, which he easily avoided, "Which means you must become assassins. Now you'll notice that he's incredibly fast, mach 20 to be precise. You're looking at a being so powerful that he can obliterate half the moon in seconds.A world he's allowed to live in is a world waiting to be destroyed. Plain and simple."

"He makes it sound so grim, doesn't he? Cheer up! I've graciously made your government an offer. Stop making fools of yourselves trying to kill me, I said, and let me teach class 3-E at this illustrious institution!" the new teacher said.

"We didn't have much of a choice. We have no idea what his motives are. But we agreed on the condition that none of you students will be harmed in any way. The advantage is two-fold. On the one hand we will know about his whereabouts, and on the other hand he will be in close range to 30 people with the means enough to kill him."

Everyone had a bunch of questions in their mind, but got distracted hearing Karasuma's words, "Do the deed and you'll get 10 billion. Kill him and save the earth. He doesn't think you can do it - use that. Green stripes indicates he's feeling superior...we have some experience with it."

"Truth be told, I'm not worried. The military couldn't kill, why would anyone assume students could?" the teacher said.

"The weapons you'll be provided are harmless to humans, but extremely fatal to him. And it goes without saying, it should be kept between us. The clock is ticking."

After days of trying to attack the new teacher, the class decided to call him Koro-sensei, since he was almost unkillable.

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Karasuma joined to teach Physical Education in order to train the students and sharpen their moves.

"This isn't recess kids. From now on gym class will be about the basics - stabbing, correct use of firearms and everything you need to succeed. Alright, that ought to do it for today." Karasuma said and ended the class.

The bell rang and the students were going back to their class.

"Ugh, now we've got quiz in the sixth period," Tomohito sighed.

"I don't even have the energy to use my brains now. Not that it's gonna change much," Y/N whined.

"They should just let us go home after gym," Nagisa said.

As soon as they reached the staircase, a figure loomed over them. A guy with red hair, standing on top of the stairs with a sly smile on his face. "Nagisa, what's up? It's been a while," the guy said.

"Karma?" Nagisa said, "You're back?"

And that was the first time Y/N laid eyes on him. She knew judging someone on the basis of appearance is something that an assassin should avoid but, she couldn't help but feel that he was...not supposed to be here. He was smart, witty but...dangerous. Sure, he was smiling but she could feel the mockery behind the smile. Not the kind of mockery that they faced from other classes, but she felt that 'amused' is what can be best described his smile as.