Assassin name : Childish Devil (Karma x OC)

A new student come at Kunugigaoka. Of course, this student got send into the End Class so "he" is necessarily an assassin ; the name that Rakuen Tokoyami got in this world : Childish Devil.
Is this "Devil" able to kill Koro-sensei ? And what dark secrets does Tokoyami hide from most people ? What will Tokoyami do about it and how is this assassin going to act ?

And this a Akabane Karma x OC because I'm obsessed with him but who isn't ?