Mawaru Penguindrum, Mekakucity Actors Recommendations
confusing plot line, characters with mysterious past, both aren't from the same studio but have somewhat similar style of animating and unveiling the story
Both have a similar feel in atmosphere and art. Also, the way the characters are connected by an unearthly force is present in both stories.
You'll have to pay close attention throughout the anime to fully understand the ending. Both anime have a colorful assortment of characters with an eye-catching art style and both are overall heavily story driven.