Isekai Sax: The Jazz Princess' Heart in Harmony – A Gender-Swapping Fantasy of Magic and Music

This story revolves around the contrast between the "Garnet Prince," a feminized boy who transforms when he falls into darkness while retaining a male heart, and the "Cobalt Princess," a feminized boy with a female heart who transforms when his maiden spirit awakens.

Sharp harbors a desire to live a yuri-filled life as a girl, so he infiltrates an evil organization’s lab, steals a magical potion, and transforms into a woman while keeping his male heart intact. On the other hand, Largo, who possesses the heart of a woman, switches bodies with his childhood friend Forte and begins to awaken to his maiden spirit.

Sharp boldly faces new experiences unique to women—like going to the bathroom, bathing, menstruation, and makeup—while Largo gracefully navigates through them. Though they build a friendship, as Largo is gradually accepted into female society, Sharp starts to feel increasingly isolated.

The reason the evil organization seeks to create feminized males is that those with male hearts are more easily drawn into darkness and can awaken as powerful weapons of war. The organization plans to send an army of feminized males to the battlefield, altering the nature of warfare. They pour their efforts into researching how to feminize men and break their spirits.

Sharp, now fallen into darkness, engages in repeated acts of destruction. Largo, in an effort to save his soul, picks up his saxophone and uses music magic to reach out to him.