Dimension Totsu Lovers!!

200 years have passed since humanity was driven to the brink of extinction by the “monsters”—anti-reality disasters unleashed across the entire globe by the Black Train. Japan has been rebuilt by an anti-reality organization known as the “Academy”.
Yet darkness always lurks beneath a peaceful world. There are outlaws called “Mages” who cast aside human decency in the name of pursuing truth. The protagonist, Houzuki Enju, is one such Mage—and an enemy of mankind.
“My son, infiltrate the Academy and assassinate Yoruno Sakura, the student council president.”
Enju is stunned by his father’s order. Until now, he has done nothing but bury himself in magical research, with not a single friend. Socially awkward and utterly naive to the outside world, he has no way to pass himself off as an ordinary student and sneak into the Academy.
But what shocks him even more is the name Yoruno Sakura. It is none other than the girl he fell madly in love with at first sight just days earlier—the girl of his first love.

Translated from Official website