Base-Breaking Character: Miu, being an attempt at an anime Cartman. The show tries painting her as a hilarious Bratty Half-Pint, but some fans feel she misses the mark, as she is an obnoxious bully on occasion. Others find her brilliantly funny.
Crosses the Line Twice: In "Matsuri in Rehab", Miu is hit on the nose with a rubber band, is kneed in the shin, then gets dizzy and falls flat on her face, all within two pages. The other girls think it's funny.
No Yay: Occasionally Nobue's Cuteness Proximity manifests in creepy ways, like staring at Ana in the bath or trying to kiss Matsuri. Chika tries to keep her sister from doing anything she might regret, while Miu just cracks jokes about it.
Memetic Molester: Nobue. Sometimes her affection for Ana and Matsuri seems not entirely innocent.
Memetic Mutation: Ana's facial expression (Google "gununu" for details) has become a popular visual meme.
Moe The whole cast, really. The English dub just takes this further casting younger girls near the characters' ages with all the adorable squeals and voice cracks that implies.
Superlative Dubbing: The studio opted for the uncommon practice of hiring actual girls very near the ages of the characters to get a more authentic dynamic among the cast. And it works. Unfortunately it means the chances of the OVAs getting dubbed are very, very unlikely.
What Do You Mean, It's for Kids?: While the series is fairly light-hearted and is serialized in a Shōnen magazine, one of the main characters is Nobue Ito, a character who engages in frequent smoking and drinking. This is less of an issue in the anime (where she is depicted as a 20-year old adult), but in the original manga, she is only 16 and still in high school (which is stated on the very first page of Chapter 1). Chapter 41 also reveals that she has been smoking since at least 7th grade, and was only dissuaded from trying it as an elementary school student after reading the warning label on a cigarette box she picked up.note Perhaps incidentally, she is seen smoking significantly less after this chapter.