When he was three years old, Eijiro woke up in the middle of the night to use the restroom. When he rubbed his eye, his Hardening Quirk manifested for the first time.
This made his hand harden and caused Eijiro to cut himself, which left a scar on his right eye. He is 16 years old now.
With his pointed red hair, mouth of sharp teeth, hard skin and claws, and his brawny appearance (and some iron themes), Kirishima is oddly reminiscent of ogres in Japanese mythology.
These beasts have horns, fangs, and iron clubs, and are often red. His favorite food is meat. Kirishima suffers from depression and anorexia after an accident that involved his brother.
His grades are slipping and he is about to lose his football scholarship, so his teacher assigns him a tutor: Bakugou Katsuki. Bakugo usually thinks of him as a rival.