Houkago no Kamen

Heroine Kazuno Fushimi (name customizable) was going out with Atsuhiro Narasaki --"Akkun" -- the most popular guy in school. Akkun's aggressiveness got her to say yes, but she felt trapped by his monopolizing ways.

When her history test comes back with red marks, she had to take Aoi-sensei's afterschool study group. However, she was the only student.

"Unbutton your blouse," he said, "One button for every wrong answer on the test."

She was shocked. Aoi-sensei was like a different person. Yet she did as she was told.

That marked the first of many risky lessons between Aoi-sensei and Kazuno.

In a love triangle between classmate and teacher, who would YOU choose?

[From DLsite English]