Shigami's Secret by @TheDevilCat (Caitlin Wilt)

Shigami reveals the reason why he wears his hair to cover half his face: a horrid mass of burn-scarred flesh, gained as a youth, when he lacked the ability to be able to heal such a terrible injury.

His mother's powerful regenerative magic restored his lost eye when he returned home, but the scarred mass on the right side of his head with always remain. The injury does not shame or disgust him, but since it upsets others, he keeps it covered for their sakes.