It's main character is Miki. Her parents had gone on a trip to Hawaii and when they returned, they announced the shocking news that they were going to swap partners with this other couple they met on the trip. Miki of course is devastated that her parents are getting a divorce, and super angry at the thought of such a strange situation. Turns out that this other couple has a son, Yuu, and he has no objections to this at all, which infuriates Miki. Of course, feelings between these two um.. stepsiblings develop...
Okay, so they get together, but just as soon as they do, something happens like an old or new flame and then poof they're apart. Side characters include an old girlfriend of Yuu's and a childhood friend of Miki's. A side story also deals with a student and teacher relationship which sort of sombers up the story a bit due to the seriousness factor.
Personal Thoughts:
MARMALADE BOY
Okay, this manga is pretty old, but I just read the manga translations recently and the plot is really soap opera like. Not a bad thing though... it's just funny trying to see through all the love triangles. The drawings are average... the story gets sorta confusing when they try to explain about the parents but it turns out to be a happy ending so what do I care?