Sex is neither male or female but gender identifies as male. Members of the Yatagarasu tribe choose their sex at the age of 16.
When he was accepted into UQ Holder's immortal squad "numbers" he was given the number 11.
Kuroumaru is in love with his partner, Touta Konoe, but when he finally confessed, Touta mistook his feelings and said he loved him back, along with everyone else in their group. For awhile, Kuroumaru started to question his gender, wondering if he really did want to become a woman after people consistently told him he should just become one if he wanted Touta to return his feelings. He later discovered that wasn't the truth though, that instead, he wanted to be someone who could stand by Touta's side and be strong enough to protect him.