The Demon Hero: Deku

Izuku spent his childhood learning Thunder Breathing. It was a technique used to slay demons. Demons were long forgotten as quirks rolled in, demons faded out of existance. Or so it was thought. Muzan, who was surprisingly alive even after thought to be killed appeared infront of Izuku in a dying state.

Muzan offered Izuku strength at the cost of the inability to be in the sun. If strength meant he could save people, then Izuku was all for it. He already had a Demon Slayer mark, so his appearance was odd already, mix that in with his 4 new eyes and you get an even stranger look. Not that anyone would care, he live in the age where mutations were normal-ish. Oh, he also had markings covering his body with mouths on his limbs (I will draw another pic of his lower body)

Being a Demon meant that he possed a Blood Demon Art. Cresent Moon Blades was the name of his Blood Demon Art.