Yuki Nee-chan no Kannou Gokko.

First year high-school 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....