GEGEGE NO KITARO

Nearly twenty years into the 21st century, people have forgotten the existence of Yokai. When a number of unexplainable phenomena plague adults of the human world with confusion and chaos, thirteen-year-old Mana writes a letter to the Yokai Post in search of answers, only to be greeted by Ge Ge Ge no Kitaro... (Source: Crunchyroll) — Description from AniList community (anilist.co).