Sei Kyou bought Rankai off a black market merchant. Rankai is the child of a rare gorilla species that has never been seen before. Initially he only raised him because he was interesting. But in just a few years he grew into a giant monster. Sei Kyou then put him though torturous training ever since his childhood. He then obeyed anything he said no matter what it was.
Rankai is a huge gorilla-like ape that resembles a human. He wears a blue hanfu with a black and red belt. His arms almost reach the ground due to his disproportional body. He has a hunch back and his feet a very large with animal like toes.
Rankai has shown to be scared of Sei Kyou or at least scared of getting punished, which eliminates all other fear. As proven when he was scared of Shin and the mountain men and Seikyo threatened him that he will get punished.
He also seems to like to play with his victims and ruthlessly kill his "toys".
Rankai first appears when Sei Kyou and Ketsu Shi are meeting. With one hit, he kills the soldier, Ton, by slamming him against the wall. Sei Kyou lets Rankai play with captives but the ape-like man ruthlessly kills his "toys" by picking them up and smashing them around.
- He's got one of the highest war/strength shown stats in the manga with 99/100 which is superior to Ouki's 98/100 and matching Moubu's. The only one that surpassed him is Pang Nuan(Houken) with a perfect 100/100 stat.