Introduced during The Captain Amagai arc, is one of the clan leaders serving the Kasumiōji Clan. He appears to be the main antagonist of the arc, apparently replacing Sōsuke Aizen.

Kumoi is seen in two outfits. The first is a white kimono with a purple wrap, looking similar to a sweater. The second is the standard Shinigami uniform with a red kimono over it. He has white hair slicked back, large sideburns, and one spectacle in his left eye. When smiling, it is noticeable he is missing a few teeth on the right side.

Kumoi often adopts a smiling and benevolent expression in front of public appearances, which belies his evil and cunning nature. He was believed to be power hungry, wanting to take Rurichiyo's position as the head of the clan, but was revealed to work for Shūsuke Amagai.