Tsumi to Batsu no Spica

Hatori is an ordinary teacher leading an ordinary life at an ordinary high school. One day, he notices that one of his students, Spica Tsumugi, is being bullied. On his way home from school, he ends up alone with Tsumugi in the rain. Hatori calls out to her, “Sensei will help you!" But Tsumugi gently takes his hand and says with a smile, “Hatori-sensei is such a liar."

Teacher and student… two people who should not get too close. The seductive girl that will turn Hatori's ordinary life upside down…

(Source: Kodansha, translated)