Although Emi and Keita have polar personalities, it doesn't mean they can't get along. However, it's only the first day of high school and they have already discovered they can swap bodies with each other. Luckily for them, this phenomenon is already well-known, so they won't be seen as crazy. This also means there's a cure and solving their problems should be a piece of cake, right? Not for them.
Swapping bodies also swaps their personalities, forcing them to learn how to live each other's lives, at least until they can make up their minds.