Koro-sensei was in the empty classroom, cleaning benches that were already clean enough. Mostly because he was bored.
It was winter break. None of his students were coming to assassinate him. The ones who had shown up recently were random assassins after the bounty, and they were no challenge at all.
Just as he started wondering what to do next, his phone rang.
He took it out and glanced at the screen.
"Oh. Akira-kun. What is he up to?"
He answered the call.
Akira's voice came through immediately.
"Koro-sensei, can you come over? I have something important to discuss with you."
Koro-sensei looked excited.
"Really? Then Sensei will be there immediately!"
He arrived at the house at Mach speed and pressed the doorbell.
Akira opened the door, his phone still at his ear.
"Nuruhuhuhuhuhu! Akira-kun, what is it this time? A new assassination?"
Akira's expression was serious.
"Koro-sensei. This is serious. The fate of the universe is at stake here. We need you."
Koro-sensei fell silent.
"Is this about that Halo game again?"
Akira paused for a second.
"Well… that too. We can talk while playing."
They moved to the living room and booted up the game on the TV.
Koro-sensei suddenly remembered something.
"Oh, right. Where is everyone else?"
Akira picked up the controller.
"Ritsu is resting in her pod. Erika went out to buy some clothes for her."
Koro-sensei tilted his head.
"She went alone?"
Akira sighed as if he had been terribly wronged.
"Well, I did want to go with her. But she said it was girls' clothing, so I should get lost. And here I am."
Koro-sensei looked at him.
"I was asking about whether she took Ritsu-san with her. Not you…"
Then the game started, and they completely forgot about the important matter.
"Koro-sensei, cover me! I'm going to push through here."
Koro-sensei panicked.
"Wait, Akira-kun! There are so many enemies there! If you kill all of them again, they might report us for cheating!"
Akira replied seriously.
"That's just a skill issue. Don't worry, Sensei. I'll hack into the server and get us unbanned again."
They kept playing, losing track of time. Koro-sensei ended up doing most of the talking, telling Akira about what had happened during his winter break.
Akira asked, "So, your hideout was discovered by some assassins, and then you saved a blind woman by curing her cancer and restoring her sight?"
Koro-sensei continued playing as he answered.
"Yes. A tumor was causing her to lose her eyesight. I just had to remove it using my tentacles."
They continued talking and playing.
Then the door opened.
Erika walked in, carrying clothes for Ritsu.
"I'm back."
She put them down and looked at the two of them sitting on the couch.
"Akira. Did you tell Koro-sensei about that important thing?"
Akira froze. Only then did he remember that the fate of the universe was at stake.
"I forgot about it… I mean, I was planning to tell him after the game."
Silence fell over the room.
Erika snapped.
"Stop playing that game! This is important!"
Akira whined.
"But this is an online game. I can't pause it!"
Erika placed a hand on his shoulder.
"AKIRA…"
Akira sighed.
"Fine…"
Out of sheer pettiness, he kicked everyone else out of the game first before leaving himself. Then he stood up.
"Alright. Since this is an important conversation, let's go to the Important Conversation Room."
Koro-sensei blinked.
"Important Conversation Room?"
Even Erika, who lived there, looked confused.
"What are you talking about?"
Akira wore a mysterious smile.
"I made a room by digging a space next to the underground lab. It's for important conversations. Let's go have that important conversation."
He led them downstairs.
---
It was a dark room. A long table stood in the middle, with two chairs facing each other. Two hanging lamps illuminated only the seats where Koro-sensei and Akira sat, both striking the Gendo pose.
They looked serious, as if they were about to discuss something important.
But they didn't.
Koro-sensei waited for Akira to begin. Akira had no idea how to start. So they remained in their poses.
Erika stood beside him.
"What are you two doing?"
Akira maintained his pose.
"Aura farming."
Her hand tightened on his shoulder.
"Akira…"
"Fine, I'll try."
He sighed, looked at Koro-sensei, and blurted it out.
"Koro-sensei. I am the Armored Titan, and she is the Colossal Titan."
Koro-sensei shot to his feet in shock.
"Nani?!"
Erika immediately pinched Akira's cheeks.
"Stop joking around!"
Akira whined, flailing his arms.
"I'm not good at this, alright?!"
She pinched harder.
"You're the one who volunteered to tell him. Now tell him properly!"
He sighed.
"It's harder than I thought."
He looked at Koro-sensei with a serious expression.
"Koro-sensei. Do you remember the first time we met?"
Realizing that Akira was finally getting serious, Koro-sensei sat up straight.
"You two suddenly appeared right next to me while I was reading…"
As Koro-sensei remembered what he had been reading, his face turned pink, and he looked away.
"I was busy with something."
Akira didn't press him on it. He already knew what had happened, so he simply gave Koro-sensei a mysterious look.
"Have you ever wondered how we did that?"
Koro-sensei thought about it before answering.
"Sensei knows it wasn't cloaking technology. I would have noticed it… But Sensei also knew that you would bring it up yourself when you were ready to tell me. So I've been waiting."
Akira smiled.
"Then the time has finally come. I'll tell you the truth. Koro-sensei, are you familiar with the multiverse theory?"
Koro-sensei thought for a moment. He was already beginning to understand where this was going.
"It's the theory that our observable universe isn't the only reality, but one of potentially countless parallel universes."
Akira nodded.
"Exactly. We're from a different universe. And we really did teleport here…"
Koro-sensei stared at him without speaking. His expression grew strange. It was an incredibly difficult thing to believe.
"Akira-kun, it's not that I don't want to believe you, but…"
Akira nodded as if that were only natural.
"I know it's hard to believe. But don't worry. I have a way to prove it. You see, Erika is a vampire. Erika, show him your wings."
Erika stared at him.
"What?… I'm only part vampire. I'm a dhampir. And why should I show him my wings? Do something yourself."
Akira turned to Koro-sensei.
"Well, I'm a… I'm a…"
He had no idea how to describe himself accurately, so he turned to Erika.
"How would you describe me again?"
Erika fell into deep thought.
"How about a… magical space elf?"
Akira gave her a strange look.
"Why an elf? I don't have long ears."
Erika explained with complete seriousness.
"Well, elves are born from a tree. Your entire bloodline originated from a tree. And you live for a long time."
Akira replied flatly.
"It was the Imaginary Tree."
Erika nodded.
"That's why you're a space elf."
Akira stared at her.
"What about the ears, then?"
Erika answered righteously.
"That's the magical part."
Koro-sensei finally came back to his senses.
"Wait, wait. Erika-san is a vampire, and Akira-kun is a… space elf?"
Erika emphasized the important detail.
"Magical space elf."
Akira tried his best to explain.
"I'm not a magical space elf… I'm a… space… It's complicated, okay? Anyway, Erika. Show him your wings."
Erika crossed her arms defiantly.
"I won't! Why don't you show him your magic?"
Akira answered seriously.
"Magic is forbidden."
Koro-sensei tried to mediate.
"Both of you, calm down."
Neither of them listened.
Then they heard Selena's voice.
"For the love of… Is it really that hard to explain such a simple thing? Fine! I'll do it myself."
Koro-sensei looked around in confusion.
"Who's speaking?"
Akira and Erika looked at him.
"You heard that?"
Purple light flooded the room, gathering into the shape of a girl. A moment later, Selena stood before them.
Selena opened her eyes. They were the same as Akira's. She wore a dress that looked straight out of a fairy tale.
She smiled at Koro-sensei.
"Nice to meet you. My name is Selena Theia Starlight, princess of the Kingdom of Asterisia. I've always wanted to meet you in person, Koro-sensei."
Koro-sensei looked at her closely.
"You look like Akira-kun."
Selena smiled.
"You've got it backward. He looks like me. I was born before him."
Akira immediately interrupted her.
"A few minutes before me doesn't count. Anyway, Sister, how are you even here? I thought you couldn't leave the castle."
Erika chimed in.
"Yeah. Can you leave that place now?"
Selena explained, "This isn't my real body. It's just a projection. My real body is still sitting on the throne."
She placed her hand over Erika's, but it passed straight through her.
Akira suddenly remembered something.
"Oh. That. I didn't expect you to be able to do it in another world."
Selena turned to him.
"I can do it wherever you are, though only for a few minutes."
Erika asked, "Have you used it before?"
Selena smiled mischievously.
"Yeah. Back when he ran away to the moon and threw a tantrum because he didn't know how to confess to you—"
Akira cut her off.
"Alright. Let's stop right there."
Koro-sensei finally spoke up.
"So you're the twin sister Akira-kun told us about."
Selena turned to him.
"Yep, that was me. I know this idiot brother of mine won't explain things properly, so I thought I might as well do it myself. Besides, we can treat this as a parent-teacher meeting for both of them. I can act as their guardian."
Akira protested.
"What guardian? You're the same age as us!"
Selena pouted.
"I'm older. So that's that."
She kicked Akira out of his chair and sat down in his place.
"Now get out of here. I want to have a proper conversation."
Akira, having been unjustly kicked aside, screamed, "Hey! Why did you… Wait. I thought you couldn't touch anything!"
Selena settled into the chair confidently.
"I can touch you just fine. We have that twin connection, remember? Now don't disturb me. I don't have much time."
She looked at Koro-sensei with a smile.
"Now, Koro-sensei. What would you like to know? Where should I start?"
Akira realized the trap and was about to stop him, but Koro-sensei answered before he could.
"Perhaps you could start from the beginning?"
Akira sighed.
"I was too late."
Selena smiled and began.
"Alright. In the beginning, there was nothing…"
She explained everything, from the origins of the Imaginary Tree and the Sea of Nihility to the war between the Asterians and the Oblivions. She also told him about the history of the Starlight family, Akira and Erika's backgrounds, and their current situation, including the black gate inside the tentacle space that threatened to destroy the world.
After hearing everything, Koro-sensei asked, "So not only will I explode and destroy the Earth, but now there's also the danger of me turning into that pseudo-Oblivion and destroying the entire multiverse?"
Akira shook his head.
"Not exactly. I mean, it's the gate that threatens the Imaginary Tree, not you. Besides, you might not even be the one who becomes that gate creature."
Koro-sensei tilted his head.
"What do you mean? Is there anyone more connected to the tentacles than me?"
Akira and Selena exchanged glances. Finally, Akira silently placed a manga in front of him.
Koro-sensei looked down at it. The title read Assassination Classroom, and his own face was printed on the cover.
He stared at it in shock.
"This is…"
He began reading all the volumes at Mach speed. Once he had finished, he simply sat there in silence.
"Akira-kun. Did you write this?"
Akira shook his head.
"No, Koro-sensei. It's a manga from my world. It's about you and this world."
Koro-sensei looked at him.
"How is that possible?"
Selena answered, "Anything is possible within the Imaginary Tree. Every possibility exists as a world there."
Koro-sensei immediately asked, "What about Naruto? What about Goku?"
Akira replied, "They're real too, though I haven't visited those worlds."
Koro-sensei leaned forward.
"Really? Then the food from Toriko is real too?"
Akira smiled.
"I've been to that world. The food there is great. In fact, that Energy Bar Beta you ate that day? I made it with Rainbow Fruit."
Koro-sensei looked shocked.
"What?! Wait, do you have more?"
Before Akira could answer, Selena interrupted them.
"Excuse me! Could you two concentrate on the conversation? I don't have much time!"
They immediately stopped.
Koro-sensei looked down at the manga again.
"What about the ending?"
Akira looked awkward.
"Well, that's it. It hadn't been released in my world yet. Though I heard it was going to be bittersweet."
Koro-sensei fell silent before finally speaking.
"Yeah. I can see that…"
Nobody said anything for a while.
Then Selena spoke up.
"Now, Koro-sensei. According to our predictions, the one who might become the gate creature… Let's just call them the Gatekeeper… is your student, Reaper 2.0."
Erika added, "He's stronger and faster than you."
Akira continued, "And after hacking into their computers, I discovered that they'd already started experimenting on him to turn him into one."
Koro-sensei asked, "So, how are you going to save the world?"
Akira answered honestly.
"With the power of love."
Silence.
Absolute silence.
Nobody knew what to say.
Finally, Koro-sensei asked, "What?"
Akira explained, "Stellar Radiance is powered by love and other positive emotions."
Koro-sensei frowned thoughtfully.
"But, Akira-kun, I have a question. You said that to complete the seal, you have to increase your calculation speed, right?"
Akira nodded.
"Yeah. Apparently, to complete the seal, I have to retrace the path it took and basically create and install something like an antivirus in the world barrier. So it requires an extremely high level of calculation."
Koro-sensei continued, "But… you told me that increasing your calculation speed suppresses your emotions. And Stellar Radiance requires positive emotions, doesn't it?"
The room froze.
They had spent so much time figuring out how to close the gate that none of them had considered the most fundamental problem.
How could Akira use Stellar Radiance when the calculations required to save the world would suppress the very emotions that powered it?