It is an anime i am recently trying to find an anime i used to watch long backit had a background where some alchemist(something similar) fighting monsters the mc is a highschool student who got killed by one of the monsters but a girl who is an alchemist uses some machine to revive him however it turns him to a weapon or superhuman which gives him a lance (spear?) when he activates its power . The mc had an appearance somewhat similar to komuro from highschool of the dead and also he dates the girl who saved him. One of the main antagonists in the anime was a guy who wore a black male ballet suit and a butterfly mask and is obsessed(something close to it?) to the mc and to fight him.
I literally just filled in 'anime butterfly mask villain' and was traumatized by the images that showed up.