Kousuke is Ataru and Hokuto's best friend and the three of them are often seen causing trouble together.

Like Shuutaro Mendo and the other male students, he is also in love with Lum and will try to prevent her from kissing Ataru, trying to protect her purity. In the later half of the series, he and Hokuto begin to become victims of the daily shenanigans. In the anime he only ever appears as a background character, and his roles are always given to either Megane or Perm.

(Source: Urusei Yatsura Wiki)