X-Change is a series of eroge visual novels produced by Crowd and translated for North American release by Peach Princess. The plot revolves around a male protagonist as he changes gender through some unfortunate means and attempts to get back to his male self. The original series had three games produced for it and an offshoot series involving a similar situation was produced by the same company, although it involved different characters. Upgraded versions of the original game were produced by Crowd, but haven't been released in English.
X-Change: The first game revolves around Takuya Aihara, a student specializing in chemistry, as he is transformed into a female in a small lab accident. The number of characters in the game is limited compared to the others and most of the storyline revolves around Asuka Katakiri and Asami Satoh, both of whom are students at his school.
X-Change 2: The second game, which continues the story of Takuya Aihara, takes place one year after the first. This time more characters are added, though primary relation revolves around Asuka Katakiri. Asami Satoh does appear in the game, but only as a cameo appearance. Chisato Kawahara takes her place as the secondary female character, though there are a lot more in this game.
X-Change 3: The third game in the trilogy takes place one year after the second game, at a different school. All the major characters are back in this game, including Asami Satoh. The main plot still heavily revolves around Asuka Katakiri, despite the new characters.
Yin-Yang! X-Change Alternative
Yin-Yang! X-Change Alternative: The plot follows a similar line as the main series, but the main character, Kaoru Sakurazuka, has an entirely different personality having a macho attitude and effeminate features. The game has a higher percentage of endings with the protagonist staying female than games from the other series.
Yin-Yang! X-Change Alternative 2