He is a friend of Tsuzuki's, and can manipulate shadows.
Seiichiro Tatsumi is created Yoko Matsushita, and he has no information regarding any inspiration used to create him. Her Japanese seiyuu is Toshiyuki Morikawa, his American voice is Walter Pagen, and his Italian voice actor is Marco Balzarotti.
He can manipulate shadows, and this is seen in the anime, Kyoto File arc. Seiichiro fends off Muraki's demons.