Mariko Izumo

The Oni-Baku meet Ayumi and Mariko at Yoron Shima in volume 1; Eikichi sees it as a chance to 'get lucky' and is constantly trying to grope Mariko.
With the revelation that the two women are not students as they claim, but are actually teachers at their new school, Eikichi initially seeks revenge on Mariko but eventually they get along. When Ayumi leaves, Mariko remains an occasional member of the SJG cast and mainly helps the pair out of difficult situations. She is also the daughter of a Yakuza boss, and a former member of Kadena Nao's 'Purple Haze' gang.

(Source: Wikipedia)