Marmalade Boy, Vol. 1 (Marmalade Boy, #1)

All Miki Koishikawa wanted was an ordinary family and that's exactly what she had until her parents decided to move in with another couple (as in switching spouses!) and turned Miki's world upside down. Now she lives in a house with four parents and her totally cute stepbrother, Yuu. It's bad enough being brought into her parents' strange soap opera, but Miki will star in a soap of her own as she deals with friends having affairs, trying to survive in school and ending up torn between her long-time crush, Ginta, and her new stepbrother!