

The Tales of Ba Sing Se from S2E15 of Avatar: The Last Airbender.
It is an incredibly poignant, albeit beautiful tableau about the loss of a child in a filler episode of a Y-7 Nickelodeon show. On top of that, the voice actor whose character is at the center of this incredibly painful story was dying of esophageal cancer during the recording and the episode ends with his in memoriam.
Whoa, I was not expecting that song to be so good. Thank you for this.