Nobody's making you sit through a narrative. A single song, animated once, designed to be exactly as long as it needs to be and no longer. The visuals exist to let the music land, not the other way around. This is what happens when you stop asking animation to justify itself and just let it breathe alongside sound. It hits because it refuses to overstay.
Oto no Niwa is a one-episode music video made for the Fujifabric song of the same name. The piece was featured on Minna no Uta, a program on NHK. The animation serves as a visual companion to the track rather than a standalone story.