Am I a demon?

Izuku yagi was once a happy kid playing with his sister and god sister when he stepped in to protect a girl with sky blue hair from his sister and god sister even though the doctor told him that he was quirkless out of his back grew a black wing as big as All Might himself out off his right hand purplish black flames licked his hand on the ground around him turned to a black corrupt soil while the wind around him turned a shade of dark purplish smoke.