I’m Milady’s Toy

Tsubame was once an impoverished and abused boy living on the cold streets. However, thanks to the compassion of a girl called Konoka Shirakamizawa, the heir of a rich conglomerate, he was rescued from his destitution and brought back to her mansion, where he was healed by their revolutionary medical technology.

With the help of big-breasted maid Morisaki, Tsubame must work as Konoka's servant. He becomes responsible for her everyday needs, from washing her clothes to managing her education. Unfortunately, Konoka—being the spoiled girl she is—refuses to study until she can satisfy her immense lust. This is worsened by the fact that Konoka used the medical technology at her disposal to modify her genitalia to that of a man! Of course, it's up to Tsubame and Morisaki to satisfy her.

(Source: MAL Rewrite)