Hen is a three-volume set of short stories that Hiroya Oku published in 1988. All of the stories are fun to read, but one story in each of the first and third volumes contains a gender-bending theme. These are two of my all-time favorite stories. There is also another series of books published in eight wide-volumes by the same author called "HEN", but without the kanji character. Unfortunately, there is no TG content in that series.

The first story in the first series was made into a television drama in 1996, and the second series of books was also made into a multi-part television drama immediately thereafter. They are available on DVD from Amazon Japan. They contain no TG content.

One day a guy named Toriai hooks up with a girl looking for someone to have a good time with. After a trip to the local love hotel, flash forward to the next day, and he discovers that something's not right with his body. He is slowly going through a sex change! Toriai has to find a way to undo this weird turn of events.

This story is a rewrite of the story in volume one, with new characters and a different plot. This time, Toriai is with a friend and they both become women after having casual sex with a couple of girls. Then things take a radical change of direction...