Tokonome Mamori is transferred to Mermaid - an artificial quarantine island for people with superpowers. When Mamori is attacked, a newly transferred girl named Mirei comes to her rescue. However, the enemy doesn't relent, and the two soon find themselves cornered. Just when they think all hope is lost, Mirei kisses Mamori, and Mamori transforms into a sword. Mirei then wields the sword and launches a counterattack against their foes.
