Valkyrie Drive -Mermaid-

Mamori Tokonome watches in astonishment as two girls show off their intimate relationship. Little did she know that she had to establish a similar relationship with another girl, Mirei Shikishima, in order to fight for her life.

Mamori and Mirei defeat Saejima, but are taken into custody by Charlotte and Ange. Now Mamori must prepare for a mysterious ceremony known as the Wedding.

Mamori and Mirei escape from the clutches of Welter. They soon learn the nature of the militant female-only group, and also discover a small peaceful village that is free from its rule.

Charlotte, Kasumi, and the forces of Wärter move in to take Mirei into custody, but the mysterious duo known as Lady Lady intervene. An all-out fight is about to break loose, but is halted by yet another new participant.

Kasumi leave the castle to investigate a strange Extar reading in the forest. There, she finds Mamori, Mirei, and a truly, tremendously buxom girl.

The Mermaid Festival is here! Meifeng must control the outcome of the Beauty Pageant to cash in on her illegal gambling scam, and she knows just the right person for shaking up the votes.

Akira secretly leaves the castle to go on a secret mission. He meets Torino, and decides to spend the night outside of the castle. Meanwhile, a hostage situation takes place nearby.

Akira meets Lady Lady at their secret hideout, not to detain them, but to send them on a secret mission - to unearth the "secret of Mermaid", which could be the key to escaping the island.

A mysterious new transfer named Momoka arrives on Mermaid. She immediately begins to befriend Charlotte and undermine the political stability established by Akira.

With Akira removed from power, Charlotte names herself the new Gouvernour, and immediately begins ruling Mermaid with an iron fist. Momoka and the other mysterious intruders seem to be taking advantage of this for their own gains.

Mirei faces Momoka, her former partner. Momoka reveals the events that lead to their separation, the hatred she has towards Mirei, and her overwhelming Soldier powers.

Momoka unleashes an enormous Valkyrie Effect through Mamori, overpowering Mirei. Now that nobody on Mermaid is strong enough to oppose her now, Momoka reveals her true intentions.