Katai Tayama/Relationships

Doppo Kunikida
It is noted that Kunikida has known Katai for over ten years knowing him before he began working at the detective agency. He has a very familiar relationship with Katai, knowing his habits. Kunikida isn't afraid to scold Katai.

Gin Akutagawa
It is weird to consider that Gin doesn't know about Katai and vice versa. However it is also unknown that Gin doesn't know about Katai loving her until when she was known to be the Mafioso that Higuchi was trying to catch. Even after Katai found out about Gin, he stills tries to propose to her, but she silently refused. Since then, it is unknown if they met.