Mami Tamachi is the childhood friend of Ryu Ogura, and she looks after him on his mother's request.
The character of Mami Tamachi is a main character of the manga series Sei So Tsui Dan Sha that was written by Shiwasu no Okina. It originally began publication in Hit Publishing's Seraphim Comics in 2003.
Her first appearance was in Sei So Tsui Dan Sha Volume 1 CH. 1 "Episode 1".