Yumi (ユミ) is an overweight student who is questioned about the "Paint-Man" incident together with Masatoshi. She dates him until the Sket Dan mention that he targets unintelligent, easy-to-charm girls - after which she dumps him.

Manga Debut: Chapter 1 (Paint-Mask)

Anime Debut: Episode 1 (The Campus SKET)

(Source: Sket Dance Wikia)