Goshuushou-sama Ninomiya-kun

Shungo is a normal high school student living in a huge house. One day, his sister Ryoko sends Mayu and Mikihiro Tsukimura, two siblings, to live with him to help Mayu overcome her problem. Mayu's problem: androphobia (fear of men), and Ryoko wants Shungo to help her overcome it. How? By making Mayu and Shungo share the same room, bed, and even take baths together. To make things even worse, Reika Hojo, the student-council chair, somehow ends up becoming their maid.

(Source: MU)