Natsume Yujin-cho - Season 4 Episode 4

Yobiko, a youkai that can imitate the voices of others, sneaks into Natsumes' house and asks him to call out another youkai named Karikami. Long ago, Yobiko had been watching over a woman named Youko who was meeting with a man at a nearby shrine. One day the man stopped coming, due to an arranged marriage to another woman, so Yobiko decided to use his talent to talk to the girl. Eventually, he told her the truth about the man and ran away. When he came back to the shrine many years later, he found an old letter that had been sealed shut and wrinkled. Natsume and Yobiko later meet Karikami and after returning his name, Karikami restores the letter. Unable to read human letters, Yobiko asks Natsume to read it to him. Instead of a hateful message he was expecting, it is actually a letter of thanks for telling her the truth.