The next day was raining cats and dogs, Shiniko got up hours before school started and went to school to sleep.

When class started, everyone was staring at Koro-sensei's head and Ritsu asked why his head was now 33% larger than before. He said that his head acts like a sponge and soaks up moisture. He then talked about the new transfer student that was coming in today.

"Hey. Heard anything? I mean, since you're both new. Figures you transfers gotta stick together, right?" Hara questioned.

"Actually, I do know a little bit. The original plan was for he and I to start at the same time, but it didn't work out that way." Ritsu answered and explained what they originally planned and why it wasn't possible.

"Compared to what he's capable of, well... Let's just say that I don't quite measure up." She finished and Koro-sensei had a worried look upon his face.

All the students turned around when they heard the door to the classroom slowly open, revealing a man dressed in white. He didn't say anything and walked in. Everyone stared at him, then all of a sudden, a dove appeared in his hand. He chuckled as the rest of the students were still staring at him.

He introduced himself as Shiro, and that he's the transfer student's guardian.

"No, it couldn't be the same guy, could it?" Shiniko thought, as she looked over at his direction and noticed Koro-sensei was in the corner in his liquefied form, "Seriously!"

"When might we get to greet your, uh, ward?" Koro-sensei asked.

Shiro pulled a treat out of his sleeves, he apologized that his so called "ward" was late, he started walking to Koro-sensei's desk. He stopped and scanned the class, his sight landed in Nagisa's direction, then to the back where Shiniko was.

"Something wrong?" Koro-sensei questioned.

"Not at all." He answered, as he placed the treat for Koro-sensei on his desk, "This seems an interesting group. I'm confident he'll fit in perfectly. Allow me to introduce him." He said and turned to the door.

Shiniko knew that the student wasn't going to come in from the door, she could sense his presence from the back of class and turned her head.

"Now, Itona. Come." He commanded, while all the students were starting at the door, expecting someone to walk through, but nope.

A loud crash came from the back of the room, making all heads turn, expect Shiniko.

"Just my luck, I'm gonna have to fix that, aren't I." She thought, as Itona entered the class, "So, it is him... Haven't talked with him in forever, wonder if he still remembers me?"

Itona took his seat between Terasaka and Karma.

"Victory is mine. I have proven myself stronger than the classroom wall." He stated.

"Come on! Use the door next time!" Everyone shouted.

"Only strength matters. Everything else is crap." He stated.

"I give you Itona Horibe." Shiro introduced, "Or if you prefer, just Itona."

"What happened to him?" Shiniko thought.

"Hey, new kid." Karma said, "Mind if I ask you a question? You came in from the rain without an umbrella. It's coming down in buckets out there, and somehow there's not a drop on you. What's the story with that?" He asked, all the students looked at him. He was right, Itona did come from outside, but he doesn't have a single drop of water on him.

Itona examined the class before getting up and walked towards Karma.

"Hm?" Karma hummed when Itona was next to him.

"You're the strongest one in the class, aren't you?" Itona asked. "But you don't have to worry." He said and started to rub the redhead's head, "You're still weaker than me. That means you get to live."

Shiniko tried her best not to laugh.

"You're beneath my skill." Itona said in a monotone like manner, he looked at the girl beside him and recognized who she was, he walked up to her, "Haven't talked to you for some time, we should catch up." He said while rubbing her head, she gave him a closed eye smile before he walked up to Koro-sensei.

"I only kill things that are stronger than me." He said as Koro-sensei was eating the treat Shiro gave him. "And in this case, Koro-sensei. That means you."

"I'm stronger than you by a whole order of magnitude." Koro-sensei said.

"Yeah. Sure. Not so much. Truth is you an' me are actually brothers." Itona said, making the whole class gasp.

"B-B-B-B-B-Brothers?!" The whole class exclaimed.

Itona took out the same snack Shiro gave Koro-sensei and bit off the wrapper and ate it. He then challenged Koro-sensei to a duel after school in the classroom. Everyone was blurting out questions at Koro-sensei after Itona and Shiro left the classroom. After they were done with Koro-sensei, they moved onto Shiniko and started doing the same thing. Shiniko got annoyed so, she stood up and everyone went silent.

"I'll tell you how I know him when the time is right. So for now, please keep your questions to yourself, they'll be answered soon enough." Shiniko said and sat back down and let Koro-sensei start his lesson. 

During lunch, Shiniko sat across from Itona at his desk studying and casually ate some of his snacks which he allowed. Many of the students were staring at them and whispering to each other, but they didn't mind. Then Itona took out the same dirty magazine as Koro-sensei.

"We boob men are all brothers!" Okajima exclaimed, and Kayano's group were talking about how Koro-sensei was related to Itona, causing him to turn to the group and back to his magazine.

After school, the students made a rectangle barrier with the desks and stood on the outside. Koro-sensei and Itona stood across from each other getting ready to fight. They set out a few rules: step out the boundary and your life is forfeit, and no harming the spectators, as that will count as a forfeit.

"Oh yeah, sure, whatever." Sugino started, "As if the loser's gonna stick to that without any issues."

"They will." Shiniko objected.

"Koro-sensei's all about how his students see him, remember? He'll abide by the rules out of a sense of honor. Cheating would risk throwing shade on his reputation with us." Karma said.

"Commence on my signal." Shiro said and raised his hand, "Assassination. Begin." He dropped his hand.

All of a sudden, one of Koro-sensei's tentacles was amputated and was now on the ground. Everyone's eyes were surprisingly not on the tentacle, but on Itona's hair.

There were tentacles coming out of his hair.

"Tentacles, but how?! I was right, Shiro is..." Shiniko thought as the class stayed silent.

"How is this possible?" Koro-sensei asked angrily, turning pitch black as the atmosphere in the class changed drastically. "Tell me where those tentacles came from. Why does someone like you have them?" His teeth turned sharp and his eyes glowing red.

Shiro chuckled, "What a face you're making. Does this encounter stir up unpleasant memories, perhaps?"

Koro-sensei was quiet for a bit before replying, "Clearly. You and I need to have a little talk." Koro-sensei said as his tentacle regenerated.

"Not possible. You'll be dead." Shiro said as a light emitted from the inside of his sleeves and explained what it was. They even knew Koro-sensei's weaknesses.

When the arena cleared up, Koro-sensei was on the ceiling with his molted skin on the ground. He wasted so much energy trying to avoid the attacks and regenerating himself, Itona took out two more tentacles.

As they were talking, Shiniko thought, "If they manage to kill Koro-sensei, they save world, literally, but I lose my friend..." She clenched the knife in her sweater pocket.

 As she watched Itona go for the final blow, his tentacles melted. Shinko looked at the ground and saw a couple of anti-sensei knives on the ground and realized that the one she was clenching was missing. Koro-sensei turned grey and had that unreadable face again.

Koro-sensei then dropped his molt over Itona and picked him up, "You may be exceptionally strong, but I'm exceptionally clever." Koro-sensei said and chucked him out the window. 

"Great, now I'm gonna have to fix that too," Shiniko thought.

He reassured everyone that Itona was unharmed, "In yo' face. I win. Nyah-nyah na-boo-boo. Etcetera, etcetera." He teased and started to lecture him.

Itona's eyes became red and his tentacles became black. He got back in the classroom charging at Koro-sensei, but before he could come close, Shiro fired something at him and he fell back unconscious. Shiro walked over to his unconscious, hot-headed ward and picked him up over his shoulders.

"Until graduation, his well-being falls on me. And, frankly, I also have a lot of questions to ask you, Mr. Shiro." Koro-sensei said.

"Sorry. we're leaving. Unless you care to use force?" He questioned, walking away.

Koro-sensei growled at his reply and tried to stop him with his tentacle, but the second he touched his shoulder, his tentacle melted. Shiro informed that the fabric was made of anti-sensei fibres. As he left with Itona, Koro-sensei watched from the window he broke. It started raining again.

As Shiniko was fixing the damages in the room, the students moved the desks back, Koro-sensei was at his desk covering his face. He was talking about how ashamed he was about being all serious, and that the students were to think of him as comic relief.

"But you got so serious about it. "Tell me where those tentacles came from? Why does someone like you have them." Hazama mimicked.

Koro-sensei began telling everyone his shtick. Then Irina came in and talked about the tentacles Itona had and everyone started to ask Koro-sensei about his past and why he was here or ever created.

"Sir, focus on what happened today. Why were you mad? His tentacles upset you. We've never seen you like that. Does it have something to do with why you were created in the first place? I mean, why are you even here?" Nagisa asked.

"The past won't matter when the planet's destroyed." Shiniko spoke up, gaining everyone's attention from the back of the class, "If you want answers, you're going to need to work for them. Assassin, student. Target, teacher. That's what bonds our class together. Keep trying to kill him, show him what you've learned." She left through the window after she finished and went outside to where Karasuma was.

"She's right. Nothing comes from nothing, boys and girls. If you want answers, work for them. Show me what you've learned. If we're done giving yours truly the third degree... classed dismissed." Koro-sensei said and started walking to the door, the he got embarrassed, again.

When Shiniko caught up with Karasuma, he was making a phone call. Shiniko climbed into the tree as he hung up the phone.

"Mr. Karasuma?" Isogai approached with the rest of the class behind him.

"What can I do for you? Or, rather, for all of you?" He asked.

"Um... Can you teach us more about assassination? We wanna sharpen our skills." Isogai answered.

"Hmmm. You already know plenty."

"Here's the deal, sir. We've been slacking off 'cause we figured someone else would take care of killing Koro-sensei, y'know?" Yada said.

"Yeah, 'cept when we saw Itona do his thing, it dawned on us. The thing is, we don't want it to be someone else." Maehara stated.

"It should be us. If they can just bring anyone they want to do it, then what's the point of us being here in the first place, right?"

"We may not have a lot of time left, but we're willing to work harder. Please. We want to assassinate our teacher!"

"Like Shiniko said, we have to work for any answers ourselves." Isogai finished their speech.

"All right, then. Students interested in beefing up their assassination skills can stay after class. Be ready to work hard!" Karasuma said.

"Yes, sir!" The class said.

Shiniko jumped down from her branch, "I can help sharpen their skills if you want." She offered.

"What makes you think you could help us?!" One of the students shouted.

"I can assure you that she's qualified enough." Karasuma stated, "Let's start by climbing up this rope. It's brand new and waiting to be broken in." Karasuma said with a evil grin.

"Already done." Shiniko said from the top.

"Seriously?!" The students exclaimed.

"Come on, if I could do it so can you," Shiniko said after gracefully landing on the ground, "You said you wanted to sharpen your skills." She said looking up at Koro-sensei who was sitting in a nearby tree.

When practice was over, everyone went home, not only thinking about Koro-sensei life, but also Shiniko's as well.