📍 the most notable thing about him is that he comes from a long line of assassins. his parents made all their kids go through a ton of not ethical training as children, giving illumi an extremely high pain tolerance and a plethora of strange and unorthodox skills.

📍 he's quite detached, often seeming overly casual and deadpan— he's a very easy-going person. his expression doesn't show it, but he speaks quite lightly. he is unbothered to a comical extent, and tends to come off like a bit of an airhead.

📍 he'll take contracted hits from just about anyone so long as they pay him.

📍 for ease of explanation: he has mind control. he has virtually no qualms about using his powers; if it'll serve his interests, he'll use them on enemies, civilians, even the people he actually cares about. more importantly, when illumi sees something/someone strong, he gets a strong desire to control it/them.

📍 manipulation: illumi can control the actions and speech of anyone that he pricks with one of his needles. he can control dozens of people at a time, and can make them perform complex actions.

while he can fully overpower someone's sentience if he chooses, he can also manipulate people more subtly, like conditioning them to act in certain ways over time.

📍 shape shifting: he can manipulate his own appearance at will - he can change his face, height, voice, et cetera, until he's completely unrecognizable. it's a really painful process for him, though.

📍 general assassin bullshit: he can like, ingest poisons and get his arm broken and be completely fine? it's... something. he has endured a lot of different kinds of torture training for his assassin work and thus just does not react when hurt. for reference his brother who underwent the same training drinks straight laxatives and does not shit to death