The Japanese government developed a military project where they created "Iron Princesses", schoolgirls who were altered to strengthen their body by replacing their bones with steel and artificial muscles. The Iron Princess are experts with the katana and are allowed to fight in the streets to determine the cream of the crop. Those who repair the Iron Princess are medical experts called Toui and they work to maintain and improve the girls.

Sakuradamon is an academy built to train girls like Honoka Asami, an Iron Princess and Nagamitsu Yomogi, a Toui. Asami is a mysterious and powerful fighter while Yomogi is a medical child prodigy and they have to work together if they value their lives on campus.