The Teacher Is Not Your **** Hole.

Mr. Yamano is a gym teacher at a small elementary school in the countryside. When gorgeous math teacher Mr. Kiyono transfers in from Tokyo, Mr. Yamano is lovestruck. One day, the two have to stay the night in a school office, and Mr. Yamano is so excited at the chance to get with his crush! Too bad his mood isn't the only thing that perks up, revealing his secret to Mr. Kiyono! But, turns out the seemingly chaste Mr. Kiyono is all too happy to ride Mr. Yamano's seven inches of man meat!!

(Source: Renta!)

Note: Includes the one-shot "Sake to Tobacco to Kiss (酒とタバコとキス)" and one extra chapter.