Marmalade Boy is a romantic comedy which centers around a Japanese high school girl named Miki Koishikawa. Miki's parents go on a trip to Hawaii and fall in love with another vacationing couple, the Matsuuras. The two couples decide to divorce and remarry--in other words, exchange partners. As it turns out, the Matsuuras have a son named Yuu, who is the same age as Miki. All the parents get along extremely well and decide that both families should live together in one big house. Miki is embarrassed and horrified about all this, but Yuu doesn't seem to mind and transfers to Miki's high school. He becomes an instant hit with the other students (he's handsome, smart, and athletic), but he is introverted and secretive and nobody really knows much about him.
As the story progresses, Miki finds herself falling in love with her stepbrother. But things get complicated when her good friend and former love interest Ginta (the guy with the light blue shirt over his shoulders) becomes jealous of Yuu. Then there's Arimi (at left in the orange jacket), Yuu's former girlfriend at his old school, who desperately wants him back. And that's only the beginning. Marmalade Boy constantly throws in new complications, and sometimes it can be very deceiving. But that's part of the fun.
Marmalade Boy consists of 76 half-hour television episodes, plus a half-hour movie "prequel" which was released in theatres in 1995.