The younger boyfriend is a bed beast (1 volume 1)

Publisher: Bunkha
Author: Eriori Hori
Size: 112mm x 174mm
Number of books: 1
Language: Japanese
Category: Girl manga, manga
Latest release date: 2016-01-29

Synopsis:
"I didn't think I was an older sister from the beginning."
Sakura became Mizuki's sister, a college student after her father's remarriage. I try to accept the bright and gentle Mizuki as a younger brother, but together, the bath, sleeping, and the skinship from Mizuki are just radical ...!? Familiar boyfriends, such as childhood friends, junior Kun, and teachers, represent the nature of Kedamono!