Yozakura Quartet – Hana No Uta is remarkably nuanced. It has a lot of unresolved sexual tension, some of which serves to underscore some of the bizarre conventions of anime.
Ao is a catgirl, not a human; she is theoretically supposed to be 15, but in some ways acts much younger or much older (which might be understandable if her psychology is more feline than hominid). She shows no sign of going to school, and while she demands a lot of cuddling from friends of both sexes, she shows an unrealistically small awareness of sex. She is as receptive to caresses as a lonely kitten, but frequently cares for the heroine as if Ao were a mother and the heroine were Ao’s daughter.
In particular, she allows her 16-year-old best friend to lick her nipple through her swimsuit and then carries on as though nothing had happened. If such a thing were to happen in a realistic character drama, there would have to be some social resolution.