A student at Hojo High School. He is Yuzuru's master and was born into a very rich family -- "The Renge Family". At first, Kai thinks Yuzuru is only a "TOY" for him to play tricks with, however soon he falls in love with her. Kai is very great at all sports (especially tennis and basketball). His academic results are also very great. In the manga, Kai is over-protective of Yuzuru, but loves her dearly. He proposes to her during a bath, and Yuzuru accepts. They are married at the end of the manga.