Kousuke is Ataru's classmate and best friend in manga. Like Mendou Shuutarou, Lum's Stormtroopers 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.
He has a girlfriend and in the manga's special chapter, he has received Valentine's Day chocolate from other girls and it's revealed that he's actually quite popular in school.

Never appears in the anime, and his role was instead split amongst Lum's Stormtroopers, mostly Megane or Perm. Urusei Yatsura Wiki