Class E decided to go their separate ways and reconvene the next morning. Nagisa sped home at Mach 20, carefully avoiding cameras. They probably couldn't catch him moving at Mach 20, but better safe than sorry. Last time a creature like him had shown up, the government had set a 10 billion yen bounty on its head and trained assassins specifically to kill it.

I'll save you Koro Sensei. Even if I have to die in your place to do it.

Nagisa reached his apartment building. He elected to go in through a window as opposed to the door so as not to startle his neighbors.

He reached his apartment and sat down. He was very hungry and tired. He went into the kitchen to make dinner for himself. His Mach 20 speed made quick work of all the required slicing and dicing, but did nothing to speed up the cooking.

While his dinner was in the oven, Nagisa set about cleaning up his apartment. It took barely a minute to do a deep clean.

Mach 20 speed doesn't help fill time, that's for sure. Nagisa pondered. What should he do next? He made lesson plans for the start of the next year in about twenty seconds.

Nagisa looked around, considering. He caught sight of one of his tentacles. Okuda said we need to replace Koro Sensei with an indistinguishable duplicate right before his death, right?

Nagisa considered. How do I make a fake Koro Sensei the rest of E-Class won't identify when it's stabbed?

Nagisa looked at his own tentacles. It has to be made of tentacle matter or it'll be identified as a fake the minute it's stabbed.

Nagisa used a tissue to grab a rubber anti-sensei knife. He willed himself to turn yellow and sliced off a tentacle. It regenerated quickly, leaving a squirming yellow tentacle on the ground. Nagisa picked it up and staunched the bleeding on the end of the tentacle that had previously been attached to him.

If I hold the blood in long enough, it might regenerate. Nagisa had no such luck. The tentacle just disintegrated in his... well, they used to be hands. I'll need to intervene more directly... Maybe stitches?

Nagisa grabbed a needle and thread and cleaned them with isopropyl alcohol. He turned yellow and cut off another tentacle. This time, he sewed the previously attached end closed before much blood could be lost. The tentacle remained intact and slightly squirmy for about a minute.

Not long enough... If I make the duplicate a minute before it's time for the switch, I'll be too slow to do it without being seen.

Nagisa didn't know what else to do to keep the tentacle alive. Well, time for some good old-fashioned cramming!

Nagisa sat down at his laptop and began researching medical procedures used to preserve amputated limbs. He found formaldehyde to be used in the preservation of amputated limbs. Maybe it will preserve the tentacle?

Further research showed formaldehyde to be found in nail polish, among other cosmetics. Nagisa pulled out his phone and opened the E Class group chat.

[Nagisa] Anybody have some yellow nail polish I can borrow?

[Kataoka] What did Karma do

[Nagisa] It's not for Karma

[Nakamura] Ooh, is it for you?

[Nagisa] Sort of

[Nakamura] Sort of? What kind of answer is that?!

[Nagisa] Guys, I just need some yellow nail polish

Kayano sent a picture of several yellow nail polishes to the group.

[Kayano] Take your pick

[Nakamura] Why do you have so many yellow nail polishes?

[Kayano] Because for some reason paparazzi care which specific yellow I use, and I don't want to show favoritism

Nagisa sped over to Kayano's house at Mach 20 and grabbed one of the nail polishes

[Nagisa] Thx Kayano

[Kayano] Anytime

[Nakamura] I think we're overlooking the important thing here

[Yada] And that would be?

[Nakamura] Tentacles made Nagisa act like a chick!

[Karma] Are we sure he wasn't a chick to begin with?

[Nakamura] Well, he didn't have anything in terms of bust

[Karma] Neither did Kayano, and she's a gal

[Nagisa] I AM A GUY AND ALWAYS WILL BE

[Karma] Then explain the nail polish

[Nagisa] I needed the formaldehyde in it

[Okuda and Takebayashi] You do realize formaldehyde causes cancer, right?

[Nagisa] It's also used to preserve amputated limbs

[Hazama] I can back that up

[26 people] Why the hell are you amputating a limb!?

[Nagisa] Okuda said I need to make a duplicate to replace Koro Sensei right before he dies. The best way to do that is with amputated tentacles

[Kayano] So that's why it needs to be yellow nail polish

[Nagisa] Yeah

[Okuda] Won't that leave behind a yellow shell when the tentacles disintegrate?

[Nagisa] Look, I'm trying here

[Okuda] You should use straight formaldehyde, watered down a bit

[Nagisa] Well where do I get formaldehyde?

[Okuda] I have some at my house

[Karma] You have a cancer-causing chemical just laying around in your house?

[Okuda] No way!

[Okuda] I use proper storage safety measures

[Karma] I have never loved you more

[Terasaka] Let me repeat, I am doomed

[Terasaka] Hang on Nagisa, where are you getting tentacles to test on?

[Nagisa] Places

[Okuda] Hang on, are you cutting your tentacles off!?

[Nagisa] A little bit

[Okuda] That's terrible! You need to stop right now. We still have a few leftover tentacle stem cells, we'll use those

[Okuda] You did not just run off with my formaldehyde!

[Nagisa] It works very well

[Nagisa] Even disintegrates properly when stabbed

[Okuda] This is unethical!

[Nagisa] I regenerate

[Okuda] That doesn't make it okay!

[Nagisa] Don't worry, I'm fine

[Okuda] We're discussing your overwhelming need to sacrifice yourself tomorrow

[Nagisa] I'm fine Okuda

[Okuda] I'll be the judge of that

Nagisa switched off his phone. Tomorrow will be quite a day... Nagisa went over to the oven and pulled out his dinner. While he was waiting for it to cool, he went and cut off another tentacle, then both stitched it and soaked it in a formaldehyde/water mixture. He took it out and dried it, then started a timer.

While he was eating dinner, Nagisa watched his tentacle. It took forty-seven minutes and eight seconds for the tentacle to disintegrate.

Assuming I recover from tentacle loss at the same rate as Koro Sensei, I should be at top speed by the time I do the swap if I create the dummy forty-five minutes beforehand.

Nagisa smiled. That's one problem solved. Now I just need to figure out how to get past the Shield of Earth...