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 is a cute, wholesome, yet short anime that is geared to the younger viewer. The repetitive cheesy music is kind of annoying, in addition to the predictable plot. The jokes are cute and the show contains many classic anime pitfalls, including the primary conflict: Guardian Angels taking on The Four Saint Beasts… Overall, I’d rate it 2.1 Ok for a one time viewing, but not worthy of repeated background noise due the overly cutesy and juvenile nature of the show.