Tetsu is one of Kumiko's lackeys. He is a member of the Yakuza group, and is very devoted and protective of her. He and Minoru always keep an eye on Kumiko and do their best to help her when they can. Kumiko took him in when he was a teen, calling him a "younger brother" since the family didn't accept underage kids, and he had no where else to go.

(Source: Wikipedia)