Back Stage!!
Ongoing | amano kazuki, eiki eiki, zaou taishi | 2000 released
For fans of love stage, back stage isn't called a sequel but a related series, but has scenes author couldn't put in, and scenes about older brother and the manager, shougo and rei. Also has some drawing and pages from the authors talking about how they made love stage. It's a cute, light read.
Kanga na Spoon