Yuki Nee-chan no Kannou Gokko.

First year Highschool boy Shin Yuki stumbles one day upon his naked childhood friend reenacting a sensual novel with an mannequin in an empty classroom. Yukino Kurose, a third year student, loved to reeanact stories with Yuki's help from books when she was a child, to discover how the characters in the story felt. This time she got herself a...