Gegege no Kitarou (1971)

Kitarou has settled into a quiet life with his father, Medama Oyaji, but the changing human world keeps disturbing places that once belonged to youkai. Forests disappear, pollution spreads, and old grudges awaken as supernatural beings begin striking back at people who no longer believe they share the world with anything unseen.

Unable to ignore the suffering on either side, Kitarou leaves his peaceful home whenever trouble reaches the youkai mailbox. Alongside Nezumi Otoko, Neko Musume, Sunakake Babaa, and other strange companions, he confronts spirits born from old legends as well as new anxieties created by modern society, trying to stop cruelty without forgetting that humans and youkai must somehow coexist.