My Little Assassin ( Nagisa Shiota X Dominant Male Reader)

Closer

After a good couple of minutes of everyone chit-chatting away to their hearts' content, there was a gentle tap on the door to our classroom. Everyone's attention went towards the door, as well as yours.
You could make out two silhouettes through the paper like screening of the door: One person who looked like an older male with a bit of a spiky hair do, and a larger being (Which you assumed to be another person) standing next him. You rose an eyebrow and sat up straight in your desk, squinting your eyes just to make sure you weren't losing it.
The door finally slid open halfway, only revealing the man who wore a tuxedo similar to your fathers'. He had a stern look on his face, and his eyes held a dark shade of gray in them.
As he walked in, he slid the door to a shut behind him, leaving the other person outside in the hallway. Eyes scouting the classroom and its surroundings, he made his way to the front of the classroom and turned towards the students. It was dead silent until he finally spoke after clearing his throat.
"Hello," the man says. His voice was as boring as his facial expression. You could already tell he was the type that didn't like to deal with people's bullshit; Which you admired.
"My name is Tadaomi Karasuma, but I'd be better off if you stuck with Karasuma for the time being. No, I am not your teacher, but I will be supervising you lot from time to time."

'He must be apart of the government, just like Dad,' You thought. You looked around the classroom for a quick moment before directing your gaze back to Karasuma.
'Was the whole class going to be apart of whatever's about to happen?'

"But enough with the introductions." His eyes darted over to the shadow standing outside of the classroom's door.
"You can come in, now," Karasuma states with a quick huff. With that, the door instantly slides open. What you saw standing in that doorway wasn't anything you would've guessed, even in a million years. You also heard a couple of gasps throughout the room from the female students, and hard, conflicted stares from the males.

The strange looking creature stood shoulder to shoulder with Karasuma. It's grin widened a tinge as well as a green striped pattern appearing all around that big, perfectly round head of his.
You instantly rose your hand, Karasuma along with the creature's eyes darting over to you, along with Nagisa and some other students throwing you questioning gazes.
"Yes, do you need something?" Karasuma asks.
Placing both hands on your desk and forcing yourself out of your seat, you gave the creature a look of wonder and disgust as he just continued to stare back at you with that same grin.
"Yeah, I do need something," you finally say, pausing for dramatic effect.
"What in Davey Jone's God damned locker is that thing?!" You exaggeratively shout out.

Karasuma held the same stern expression as he answered, "... This is your teacher.
From now until March he will be your supervisor and caretaker, but that isn't all."
That last part threw you off guard. You abandoned your conflicted state.
"What do you mean that isn't it?"

Karasuma's expression became increasingly serious as he continued on.
"What I'm about to explain to each and everyone of you is top secret information that absolutely does not leave this classroom. For your sake, I hope you do not take that lightly."