Abandon Shipping: Viewers were entirely sure that Jun and Kyoko would get together come the end of the anime, as that meant that not only would the path be cleared for Mion/Wataru to happen, but also that Kyoko would finally get the husband she seeks. However, in episode 41, it was revealed that they are actually half-siblings born from the same mother. But then in DMF episodes 44-46, it was revealed that they're not related after all. Her mother adopted him after his parents died in a road accident.
Big-Lipped Alligator Moment: Episode 27. You're watching an anime about girls achieving their dreams in show-biz when BAM! Random plot about returning magical dolphin to its parents right in your face!
Ear Worm: The OP (named 'You May Dream', by LISP) is pretty catchy.
Fandom Rivalry: Most prominently with Aikatsu!, but also with other idol series, such as AKB0048, Love Live!! and The Idolmasternote Which is aimed at an older audience than Pretty Rhythm or its Spiritual SuccessorPriPara. Not only that, but The Idolmaster is also aimed at older males as well.. And after the mega successful spinoff series KING OF PRISM by Prettyrhythm took off, it has some infighting of its own.
Les Yay: Lots. Episode 19 had Mion invite Rhythm and Aira (one at a time) to go on a date with her, so she could decide who would be the best partner. And until episode 22, Mion felt like she was being a third-wheel in Aira's and Rhythm's relationship.
Aira and Rhythm are always supporting and worrying about each other in their Prism Shows, so much that the usually determined Rhythm decided that she would tone down her act so Aira could follow her moves.
Until MARs had been formed, Aira always referred to Mion as 'Mion-sama' and looked at her with starry eyes. When Mion tells her to cut it out and call her just 'Mion', Aira turns even more starry-eyed and repeats her name several times, which flusters Mion.
Mion and Rhythm at times seem Tsundere towards each other.
Kaname is always hugging and jumping onto Aira and telling her how much she loves her. She has also touched Mion's chest and licked Rhythm's face.
Older Than They Think: The arcade game did not start with Aurora Dream. The first title is Miniskirt, which didn't get animated.
Sophomore Slump: Aurora Dream, the first season, is well-regarded, and the third season, Rainbow Live, is widely considered the best. But the season in-between, Dear My Future, which is a direct sequel to AD, is seen as very weak (it's telling that it doesn't even have completed fansubs, unlike the other 2).