Mahouka Koukou no Rettousei - Shiba Tatsuya Ansatsu Keikaku

The Spring of 2094 AD. A young girl whose calling is assassination, Hashibami Yuki, is witnessed by a young middle school boy at the scene of a crime.
Supressing misgivings about erasing a young middle-schoolboy, Yuki’s superior abilities cannot compete at all. The name of the mysterious boy is Shiba Tatsuya.
If the opponent was a normal boy,
If the opponent was not a magician,
If the opponent was not Shiba Tatsuya—
An "irregular" boy and an "assassin" girl. The meeting of these two will alter fate and bring misfortune.