I"s Pure - Season 1 Episode 2 Reminiscence

Kazuki is suddenly confronted by his childhood friend Itsuki, whom he has not seen in four years, in his underwear. However, Kazuki's feelings for Iori grow, and he tells her that his relationship with Itsuki is "just a childhood friend". On a school trip, Kazuki is alone with Iori and tries to pluck up the courage to confess his feelings to him, but just then a fire breaks out in Itsuki's flat and he receives a call that Itsuki has not been seen since...