Ningyo no Uta
English name: Mermaid Song
Genres: Avant Garde
Type: Movie, Episodes: 1
Aired: 2017
Source: Original
Rating: R - 17+ (violence & profanity)
Synopsis:
A boy and a girl draw pictures on the wall with sticks made of black fish. One day a blue fish drifts ashore to them.

(Source: Geidai Animation)