Sukidarake no Anta ga Warui

Mr. Murakami and Mr. Sasakawa have started their jobs at the same high school. Mr. Murakami, the math teacher, is outgoing and friendly, which makes him popular with the students. On the other hand, Mr. Sasakawa is rigid and guarded. Their relationship starts the night they go out for drinks with their colleagues. Mr. Sasakawa sneaks out early, but Mr. Murakami follows him, and demands they drink one-on-one. Mr. Sasakawa has a little too much, and can't even walk straight. Luckily, Mr. Murakami catches him before he hits the ground. But, then, he strokes Mr. Sasakawa's cheek and kisses him...! It's love at first sight for Mr. Murakami, but Mr. Sasakawa doesn't want anything to do with him! A story of frustrating romance between a popular math teacher and an uptight history teacher.

(Source: Renta!)