Illumi Zoldyck

Illumi is the first born son of the Zoldyck family. For all intents and purposes, he's the perfect assassin. Cold, merciless, and filled with deadly grace. He's the perfect manipulator, both as a nen-user and as a person. He operates on cold logic, and his morality is skewed. Obsessed with family, and shows love in his own twisted ways. (You can be anyone you want, a Zoldyck, an illegitimate child, a friend, an arranged fiancé... I'll make the opening vague enough.)