The 4 Conditions (S01E12)

At last Ricotta and her assistants come with a way for Sink to return home. However, she finds that by doing so, not only he will forget all memories and experiences of his time at Flonyard, but he will never be able to come back. Upon learning of it, Sink asks Ricotta to not tell the truth to the others, as he does not want them to send him off with a sad face. (Crunchyroll)