School Rumble

Second-year student Tsukamoto Tenma learns that her secret crush, Karasuma Oji, will be transferring to a school in America. In a last-ditch effort to reveal her love to him, she writes a long (but anonymous) love letter. When Karasuma ends up postponing his transfer for another year, Tenma realizes she has to tell him how she feels before time runs out again. But her extreme nervousness around him prompts her to try and setup all sorts of schemes to get close to him and let him know, without actually coming out and saying it. Meanwhile, unknown to Tenma, the school delinquent, Harima Kenji, has the biggest crush on her, as well as the same anxieties about being direct. Around this love triangle of clueless people are a few of Tenma's friends, and her younger (but older looking, more mature, and more popular) sister, Yakumo.

(Source: Anime News Network)

Note: This manga consists of 283 sharp chapters and 62 flat chapters. Sharp and Flat refers to the musical notations.