Nibun no Ichi Boyfriend

A rom-com gender bender about Aijiro, a young man born with the rare condition of turning into either a male or female, dependent on his heart rate along with his super rich girlfriend, Sakura Ichijo, and their endeavor to keep his gender bender trait a secret from his school and life.

Description from Oblivion Lumiere:
Soujirou possesses a special predisposition that causes him to "transform into another gender when his heart throbs." Moreover, his girlfriend, Ichijou Sakura, is an elite young lady who came to acquire the same special predisposition as well. Their love life is filled with chaotically transforming between male and female; is this normal romance or girl's love or boy's love or other!? This is a love comedy featuring transformation between male and female★

Links:

• Mangaka's Twitter
• Mangaka’s Pixiv