Chinyuuki: Tarou to Yukai na Nakama-tachi(1990)

Chinyuuki: Tarou to Yukai na Nakama-tachi

Everyone remember that classic story of "Journey to the West", where 3 travelers help a monk to right their misdeeds? This is not that story...
"Chinyuuki: Tarou to Yukai na Nakama-tachi" is a parody of "Journey to the West", where an assassin by the name of Tarou Yamada is trying to right his misdeeds by travelling with a monk. Tarou's misdeeds were essentially assassinating tons of people and pooping on their graves. A monk saw him and cursed him into a baby-monkey-hybrid-thing. With the help of the Monk, Tarou has to battle demons and other weird anomalies to help regain his human form.

(Source: TV Tropes)