After viewing this again the music gave it away. There's a lot of similarity to the character design, and musical cues on top of the OST(excluding the main themes). The plot style isn't too dissimilar, though Angel Tales has no nudity or time travel. They're also both semi-quick series AT:13 eps + a bonus while Popotan: just 12.

Angel Tales

none

All direct violence occurs off camera.
Only object destruction occurs on screen.