Shiina

Eri Shiina is a self-proclaimed ninja who goes by the codename C-7 and fights with dual kodachi and shuriken. For a long time she lived deep within the tunnel system beneath the afterlife school, acting as a kind of final boss for anyone who dared explore its depths.

Yuri Nakamura and Hideki Hinata are the first to face her and lose; it takes a combined effort from Ooyama, Chaa, and Noda for the SSS to finally subdue her and talk her into joining. Implied to hail from feudal-era Japan, Shiina is visibly out of her depth around modern technology.

Beneath her tough, tight-lipped exterior lies a genuine love of stuffed animals, a soft spot that gets her into trouble more than once. In combat, though, she remains one of the group's most formidable fighters.