Nagisa got distracted halfway through battle.
He was still a teenager right now, and being a teenager, his mind wandered when he did tedious things.
He looked to the side, noticing Iida missing.
He must've gotten help, he noted.
Thirteen was busy sucking up Kurogiri, or whatever the warp gate's name was, and Eraserhead and Present Mic were battling some rando villains.
Karasuma must've been transported somewhere else, because he was absent at the moment as well.
The assassin stabbed two villains from the side in the temple, then pulled out the blades and snuck around another, pulling the metal past his throat, successfully killing him.
A few dots of red were splattered on his face (his clothes were hydrophobic, an adjustment he came up with), but other then that, he looked normal.
Normal enough to fool some other villains into "pitying" him, then slitting the carotid artery by cutting open their abdomens.
His hands at this point were drenched in red, and only after he saw Tsuyu snd the other two swimming up to the Central Plaza did he notice.
"Eh... Karma, do you maybe have a towel?"
"A towel?" He glanced over at the blueberry, who was holding his dripping hands up. "Ne, that blood makes you look pretty deadly~."
Nagisa blushed, then huffed. "Cut it out! Towel or no?"
"Yeah, yeah," he hummed, throwing a red rag at him. "It's already crimson so you won't stain it."
He wiped his hands, tossed it back, and mumbled to himself. "I think my hands have had enough death for a day."
He looked down, eyes meeting Mineta shaking in fear. "Eh? H-hey there guys...!"
He laughed nervously, stepping in front of the small pile of bodies. "Which zone did you get sent to?"
"Flood zone," Asui croaked. "Care to explain what's going on here?"
"Oh! Okay, so Karasuma-Sensei, Present-Mic, and Eraserhead are fighting off the villains, the former being in some other zone. Iida-kun ran to get help, and some other students are behind Thirteen, who's working on defeating the purple dude."
Midoriya climbed out of the water. "So... where are the villains?"
"Huh?"
"Well... I only see that purple dude and... three other villains."
"Did you say three?" Nagisa jerked his head around, landing on... none other then Nomu and Shigaraki. "Oh god... this is too soon. Who's the third villain?"
Deku nodded at Karma. "That boy. He looks our age."
The sadist noticed his gaze, waltzing over to the four. "Couldn't help but notice you're staring at me~. Am I that handsome?"
Tsuyu jumped out of the water too, standing beside the broccoli defensively. "Get away, villain. Don't hurt Midoriya or Nagisa, kero."
"W-W-what about m-me?!" Mineta yelped, eye peeking out from the lake.
His statement was ignored.
"Oh, c'mon. You really think I'd lay a hand on any of you?" He smirked, one arm heading towards the assassin. "Nagisa here is an exception, though."
Karma's hand made its way to his chin, tilting up his face slightly, which received a blush. "K-Karma, what are you doing...?"
"You know him?" Izuku asked, blinking. "But I thought-"
"I'm somewhat of a double agent," he answered, still staring at Nagisa.
"Karma, stop!"
"Make me~"
Their banter was interrupted by the flash of a camera. "Nishishi! Another one to add to my collection!"
"Koro-Sensei... did you say... collection?"
The octopus' face turned red, a circle marking his features. "Corrrrrect! I've named the compilation 'Karmagisa Moments'!"
"Oh I get it," Asui exclaimed. "He thinks you two would make a great couple!"
He turned to the frog girl. "Absolutely right! Now, I'm going to go check on a bakery I found earlier." As he prepared to take off, he grinned again. "See you later!"
Froppy looked back at the boys, who were rendered speechless, blushing at her statement.
"Wow, he wasn't wrong."
"T-Tsu-Chan, he was completely wrong!"
"Y-yeah, we've been friends since forever."
She shrugged, then froze. "Hey... what's that creepy bird doing to Aizawa, kero?"
The assassins turned their head to where she was pointing, exchanging a glance then rushing to help him.
"Get off him, Nomu!" Nagisa yelled, jumping into his back.
Karma slid to a stop when he realized Chapstick was watching him, not willing to risk the mission given to him for the teacher's life.
He made eye contact with the assassin, unspoken words exchanged.
The sadist then rushed away towards Karasuma, who was probably nearby. On his way, he sprayed pepper spray at some villain's eyes.
Meanwhile, the blueberry was still working on incapacitating the "Anti-symbol of Peace", which proved more difficult then it seemed.
Regeneration and shock absorption were the quirks he could remember, and so the monster hardly noticed him.
When it did, it slammed him into the water, right next to the other three.
Blood drifted up to the surface, and Asui and Deku hurriedly made their way over, but before they could, he popped back up. "Damn it! No one told me that I'd have to use my quirk!"
They froze.
"Oh... one of them is regeneration. It saps my emotional energy, which tends to make me more moody right afterwards."
He climbed back up, this time running at Shigaraki.
"Ah, Shiota Nagisa, quirk, hybrid, lets him help and harm, all while having wings, a halo, and horns."
He forgot the healing and snake one.
"That's not stopping me from beating you," the assassin grinned. He released some of his bloodlust, making the villain freeze. Right as he was about to sink a knife into his chest, two voices stopped him.
"Nagisa!"
And:
"Young Shiota!"
He glanced at Karasuma then at All-Might, and lowered his blade.
Shigaraki's not supposed to die, not yet.
"Sorry..." he mumbled, retreating back to Karma and Karasuma.
"It's fine, Nagi. You'll get him next time," the sadist laughed.
"Right. Thanks for stopping me."
"I'm assuming it's a quirk's drawback?"
"Mhm, emotional instability."
Nomu on the other hand turned to All-Might, and Shigaraki stood blankly, staring at Nagisa.
"Nomu... let's go."
It looked at him in surprise.
"We're leaving."
Karma glanced at his blueberry. "You can kill the bird thing, probably."
"No, that's Toshinori-Sama's job."
"Then we're as good as done. Wanna leave?"
"No, the others will freak out if I'm not there at the end."
"So should we gather the others?"
There was no reply.
As if he sensed his student's turmoil, Koro-Sensei came quietly through the window, landing next to the two. "Say, either of you want a pastry?"
Both of them took one gratefully, and they watched the battle between All-Might and Nomu, the students jumping in to help him, and them working together.
Then, he told them to back off, smashed Nomu out of the glass, and then finally, right as Shigaraki was going to disintegrate Deku, did the pros arrive.
"You better now?" Karma asked.
"Yup... sorry I acted so weirdly... I just figured out why, and I'm trying to control it, but- oh! I should write this down!"
My weaknesses:
My quirk causes emotional instability
When this happens, I don't think through anything
All-Might de-transformed behind Cementoss' wall, luckily blocking the students (namely Kirishima) from seeing.
The people who knew about Karma didn't rat him out, so he managed to pass off himself and Koro-Sensei as captives that wanted to attend UA.
They quickly had a meeting with Nedzu, no doubt telling him about their true intentions, and he filed the forms necessary to let Koro-Sensei be a teacher, and Karma attend as a student.
The kids had a day off of school.
The next day.
Iida had all the students sit down, and Aizawa walked through the door covered in bandages.
"Nice to see you doing well," the engine hero yelled.
"If you call that good," Uraraka mumbled.
"My well-fare isn't important," he declared. "Because your fight is far from over."
"Our fight?"
"Don't tell me..."
"More villains?!"
"Yuuei's sports festival is quickly approaching!"
Everyone gasped. "That's so totally ordinary...!"
He went into a lament explaining the whole idea, answering the children's questions, and letting them talk.
"Oh. Also, you have a new student and teacher."
"What?!"
"No way!"
"Right after what happened?"
"Who are they?!"
"Come on in."
A red head and an octopus shuffled in.
"Yo. My name is Karma, and if anyone has complaints about my transfer, bring them to me."
"Nishishi! I'm Koro-Sensei, and to help train you all, please try and kill me by the end of Yuuei."
Nagisa blinked. "Again?!"
"Yup!"
"But where's the incentive?"
"Hmm... you're right! I'll make sure that whoever kills me will get one hundred million yen!"
At that, the classroom burst into noise.
"Holy-"
"That's... that's so much!"
"Are you serious?!"
The octopus' face went green with stripes. "If you can, that is."
Karma raised an eyebrow, and plopped down next to Nagisa. "What about the anti-Sensei weapons?"
He grinned, and a second later, everyone had a green knife and gun in their hands.
Nagisa and Karma wasted no time, the sadist shooting at him while Nagisa tried to force him where the bullets were.
The classroom went silent.
"Nice try, you two, but no guns in the class, remember?"
They sighed.
"Yes, Sensei."
Everyone started freaking out.
"Did you shoot at him?"
"Why am I holding a gun...?!"
"How did he move so fast?!"
"I don't want to kill my teacher!"
Koro-Sensei grinned. "Welcome to the hero-assassination class, 101, held at the end of the day!"