18+ Joshikousei Kyouhaku Inkou Nisshi: Nakayoshi Kyonyuu Pet Kyousei Zecchou Akume Ochi

Yasukata Ueda is the deputy principal of a girls school.
Surrounded by nubile beauties with no way to fulfill his desires,
he is increasingly dissatisfied.
All he does is think about sex with one of these girls.
One day he hears voices coming from the student lounge.

Ueda finds two girls secretly making out.
What! What is this? The ultimate male fantasy and he can't---
wait, he has a smartphone, he can get some video.
Before the girls catch him peeping, he slips away.

Now he has the means to threaten the girls.

He can't blackmail them both at once... but who to choose first?

The pieces of a plan click into place...
and like dominoes, Ueda's moral barriers are falling.

(Source: dlsite)