Mio is an ordinary female student. One year ago, she became a futanari and saved another world.
While living peacefully in the modern day, she reunites with her childhood friend Luca for the first time in 10 years, but fate shakes her again.
She is reunited with Seira, a saint from another world.
Seira has appeared to stop the invaders from another world that threaten the modern day.
To protect peace, Mio rises up again as the hero of the holy sword, the futanari!