Ore Monogatari!!

Synopsis

As word spreads around class about Takeo and Rinko's relationship, Takeo saves a child from drowning on his way to another date. As the pair take a stroll through the park at night, where Takeo appears to miss some subtle hints from Rinko, Makoto is visited by his older sister Ai, who is shocked to hear Takeo has a girlfriend, having had a crush on him herself. The next day, Ai brings herself along to Takeo's next date to meet Rinko, who becomes shocked when she learns she messed the cookies she baked. Rinko feels relieved that Takeo likes them anyway, but becomes downhearted when he mentions how pure she is, something Ai is keen to pick up on. Noticing Takeo realise his own denseness and putting in the effort to try and understand Rinko, Ai offers to speak to Rinko about what's bothering her. (Source: Wikipedia)