Futaba-kun Change is a manga title by Hiroshi Aro. The comic originally appeared in Shounen Jump Monthly starting in 1990 and was then compiled into 8 volumes.

Studio Ironcat started releasing English language versions in 1999. The comics have a regular release schedule, with each set of 4 being re-released compiled as a graphic novel, containing the same episodes as the original volumes.

The story follows Futaba Shimeru, a fairly normal high school student. He has a regular family, with a mother, father, and older sister, he's a member of the wrestling club, and things are starting to get a bit more serious with the girl he really likes. But there's a little something about his family that he's about to discover the hard way. He changes gender when he gets excited!

His parents are ecstatic, his sister is interested, and his girl is confused. As if puberty and high school weren't already difficult enough. Now Futaba must learn how to seem like two different people in the same gender-switching body and somehow keep his friends and school faculty from figuring out that Futaba-kun and Futaba-chan* are one and the same. Luckily, he's not completely alone. The principal is aware of the family heritage and is willing to do what he can to help keep it secret. But just when Futaba thinks he's starting to get a handle on things, that's when they start to get really strange.

This is a bizarrely whimsical tale that is fast-paced and funny. While many people compare it to Ranma 1/2 for the gender-changing antics of the main character, that's about where the similarity ends. Futabakun Change is a tale with a difinite direction and the plot advances notably with each passing issue. The mix of strange and serious is well-balanced and the art is attractive and detailed without being cluttered.
* The suffixes -kun and -chan are generally used among friends and family and carry masculine and feminine connotations respectively.