Yui Kotegawa is a high strung girl who has a very strict on student behavior, especially when Lala and Reto Yuki are involved. She often ends up in some strange situations (ending up embarrassed, naked or groped). Gradually, as she becomes accustomed to Lala's and Reto's antics, she develops some feelings towards Reto. However she is too embarrassed to admit that she likes him because of the fact she is very inexperienced with boys. A running gag is that the characters introduced later in the story can't remember Yui's family name presumably due to the fact she is generally an unwilling participant in Lala's frequent schemes. Yui is a major cat lover (everything she has, has something to do with cats eg. a cat-themed floaty)