Myself; Yourself - Season 1 Episode 8 Secret Post

Nanaka acts coldly towards Sana the following day, even after Sana explains his incident with Asami was an accident. After Sana exclaims that Nanaka is not her old self, she angrily runs away. Sana comes upon an old mailbox that Sana and Nanaka used for private communication in their youth, and finds dozens of letters, some desperate cries for help. Sana then learns from Syusuke that three years prior, Nanaka's house had burned down, killing both of her parents and traumatizing her. After learning of Yuzuki's ability to cheer herself up with caramel, Sana meets Nanaka, who tearfully denounces him for not being there for her when she needed him most.