A new teacher comes to a boys school and immediately has a young student hitting on him. Along with another student always glaring at them when they're together. So the teacher decides to go along with it and make a game out of it even though he's straight. But what starts out as fun soon elevates into the teacher trying to keep the student who admires him away.

From DramaQueen:

A math teacher unwittingly formulates a love triangle with two diabolical variables divided over him. Unhappy teaching at an all boys school, the heterosexual Amamiya entertains his bitterness by toying with an adoring student. The surprising interference of the boy's fierce former friend, however, places Amamiya at the center of a wildly twisted tug-of-war. Teacher and student: a taboo love affair gone... comedy?!