I believe the name explains the nature of this character. He is the known killer of the parkour criminals and never shows remorse in what he does.

Hotaru is the appointed antagonist of my fanfic, "I'm Onee-Chan".

The man is hot-tempered, has a sadistic sense of humor and--weirdly enough--has a lower than average amount of iron in his bloodstream. The condition is nowhere near life threatening but it does come with a few side effects. The one Hotaru suffers from the most is that he becomes cold more easily than others.

It's easy to imagine how embarrassing and unusual it would be for a bloodthirsty killer to shiver like a wet puppy in seventy-five degree weather. So, Hotaru does everything in his power to hide this humiliating physical aspect about himself.

He is also the newest "special" member in the Urban Jumpers, so his relationship with the other criminals are still quite rocky--not that he would want or care about forming relationships with them. Hotaru just wants his share of the pay, not to form life-long friendships or bonds.

It will be revealed later on in the story that he is the younger brother of Mizoku, the previous leader of the City Runners before he was killed; bringing an end to the CR gang completely.

Story Origins: "I'm Onee-Chan", K-On Fanfiction