Yuki Nee-chan no Kannou Gokko.

First year Highschool boy Shin Yuki stumbles one day upon his naked childhood friend,
Yukino Kurose, reenacting a sensual scene with an mannequin in an empty classroom.
She is a third year student who wants to experience first hand scenes from the book she reads and wants Yuki to help her!
Things get a bit complicated though as her favorite books are erotic literature….