Taisetsu na Koto wa Subete Kimi ga Oshiete Kureta (2011)

Overview

Natsumi Uemura and Shuji Kashiwagi, are two teachers at the same high school who are due to get married in six months. However, the night before the school year's opening ceremony, Shuji becomes involved with the young Hikari Saeki, without realizing that she will be a student in his class starting the next day. As Shuji struggles to help Hikari deal with the mental complex she is suffering from, he is also torn inside by his betrayal of Natsumi. Meanwhile, Hikari attempts to get closer to Natsumi, driven by feelings of jealousy and a desire to destroy the couple's relationship.