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 contain similarly confusing (initially) plots, filled with symbolism and abstract ideas. They both have very distinct visual identities, often going for style over realism. The main plots of each are not fully explained or revealed until the last few episodes, and they make the confusing build up worth the ride. If you want something to over-analyze, try either of these. They will certainly captivate you, confuse you, and charm you.
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.