From Tokyopop:
Kohamaru comes from a peculiar family—each member can switch bodies with his or her soul mate! His parents can switch bodies, and his sister, oddly enough, can switch with her cat! Now it's Kohamaru's turn...
When Kohamaru literally runs into Nanao, the girl of his dreams, they switch bodies. True love, right? Well, unfortunately, she's in love with someone else. And if that weren't bad enough, the "someone else" turns out to be Kohamaru's twin brother Konatsu...who can reverse their transformation with his own kiss!