X Change 2

Takuya Aihara, the unlucky chemistry student at Miyanomori Private School, who has a tendency to get caught in bizarre chemistry accidents that cause him many problems. When a strange chemical turned him into a girl last year, he had a bizarre string of experiences as he learned "how the other half lived." Now, one year later, he's enjoying his school life with Asuka, his steady girlfriend, but unhappy days are around the corner, as chemistry club member Chisato uses him as a guinea pig for a new experiment, which changes him into a girl once again!

(Source: Peach Princess, edited)