Shoujo Kakumei Utena, Oniisama e... Recommendations
Both series center around a naive girl adapting to her strange surroundings in a new school -- they involve many characters with deep emotional and psychological scars. In addition, both have elements of yuri.
In a lot of ways, Oniisama e feels like a spiritual predecessor to Utena. You have a classy private school setting, a large cast of primary, secondary, and tertiary characters, dark secrets, complex motivations, twisted relationships, and a unique atmosphere created by combining lush shoujo imagery and visual symbolism with music. Oh yeah, and lesbians.
Chiho Saito was probably inspired from Ryoko Ikeda's works, as these authors' styles are very alike.
Utena is especially similar to Onii-sama, as both series involve a school setting, a transferred student (Utena/Nanako) and her lively best friend (Wakaba/Tomoko), an elitist group of students (Student Council/Sorority), the beautiful and tormented school idol who wears man clothes (Juri/Rei), the rich, spoiled, blonde girl (Nanami/Aya), some shoujo-ai subtext, drama, romance, and incest.
Overall, the story, characters relationships, and feeling are the same.
The creators of Utena drew ideas from the original manga written by Riyoko Ikeda as well as the anime based on the manga. The setting in an upper class school and the new student going against the established traditions of her senior classmates, classmates which externally seem to have their lives completely togehter. Nanako has to overcome many external obstacles for her as well as her friends but most of the story revolves around the bitter internal struggles for all the characters which leads to a lot of self reflection to finally find out what she really wants as well her attempts to shatters
All I can think about while watching Onii-sama is "utena". Gives me alot of Utena vibes, especially the opening, I feel like the opening is about to play the utena opening.