Rei is Sana's manager.

Sana declares him as her "pimp" after reading a book which included the word, although she does not understand what it really means. In addition, Sana thinks of Rei as her boyfriend. Later, Akito tells Sana that Rei is playing with her, and sees her simply as a little girl wanting to play. Misako also tells Sana that Rei cannot be her boyfriend. This leaves Sana devastated. But after she gets over her heartbreak, Rei remains her manager and her friend.

(Source: Wikipedia)