Friend and follower of Mukuro, Ken broke out of prison with him. He has a scar that stretches across his face. Like Mukuro and Chikusa, Ken was also experimented on by the Estraneo Famiglia. The experimentations done on Ken involved giving him attributes of certain animals when he changes to different sets of teeth. He decided to follow Mukuro when the boy killed their captors, and offered them to come with him. He was Chikusa's cellmate in jail and often calls him "Kakipi".

When Ken changes to a different set of teeth, he could adopt the abilities of various animals, like wolves, lions, cheetahs, gorillas and even rhinoceros. He dubs his various forms "channels", comparing it to changing game cartridges. With them, his agility, strength, and senses increase. He was defeated by Yamamoto and was later defeated once again by an injured Kyoya Hibari. Despite his injured body being used by Mukuro during the latter's battle against Tsuna, he remains extremely loyal to Mukuro. He, along with the rest of the gang, was taken away by the Vendicare, but later escaped.

Ken often mocks and berates Chrome every chance he gets, showing his evident dislike for the girl.