Gleipnir

Gleipnir is a manga written and illustrated by Takeda Sun.

Plot
Shuichi Kagaya isn't human. He has an unnatural sense of smell, and can transform into an incredibly powerful beast... of sorts. He does all he can to avoid standing out and being discovered, but no good deed goes unpunished, and his decision to use his power to save a girl spells the end for his quiet life.