Aozora★Wars

Tamaki, a teacher in training, meets a rough-looking teacher at the elementary school he gets sent to. His hair is messy, he only wears track suits, and he always looks bored out of his mind... Tamaki's first impression of Hideo Ei couldn't be any worse! However, when Tamaki's supervisor, who also happens to be Hideo's sister, invites him to live at their house, he can't refuse! And thus begins Tamaki's secret lesson in love, under the watchful eye of his new mentor.

(Source: Renta!)