I actually read this manga, years ago. It was...okay? I don't remember that much now, but it was at least a palatable read. Although, I don't think I easily grasped what the whole deal was aside from the middle-school boys and girl having those sprite-like things (their official name escapes me).
Osu! is a rhythm game based off of Osu! Tatakae! Ouendan! and the American release Elite Beat Agents. In these games you click circles to the rhythm of the song. Osu! also has different rankings you can shoot for, with SS being the best (Hit every note and have 100% accuracy). There are also mods like Hard Rock, Hidden, Flashlight, and Double Time/Nightcore if you want to increase the difficulty even more.