Boku no Omocha ni Narinayo Be My Toy

Synopsis

Before Mio was born his father had a relationship with another women, the result of that relationship was Ryouichi, Mio's elder brother. Harboring resentment of not being told of Ryouichi's relationship to him earlier Mio makes Ryouichi his "toy" and Ryouichi goes along with it without complaint. (Source: MU)