Rei is Sana's manager.
After being dumped by his girlfriend, dropping out of college, and losing his parents, Rei hits rock bottom and becomes homeless. While begging on the streets, Sana finds him and brings him home, much like she does with stray dogs (in the manga, they own three). Misako decides to keep him around the house, and he has lived there ever since, working as Sana's manager.
Sana calls him her "pimp" after reading a book that included the word, although she doesn't understand its true meaning. Additionally, Sana considers Rei her boyfriend. Later, Akito tells Sana that Rei is just playing with her and sees her as a little girl wanting to play. Misako also informs Sana that Rei cannot be her boyfriend. This news devastates Sana. However, after she recovers from her heartbreak, Rei remains her manager and her friend.
(Source: Wikipedia)
