Ep. 8: The girls investigate a secret location and battle an Artificial Arm while Mamori transforms to aid Mirei.

8

Akira tasks Lady Lady, Mamori, Mirei, and Meifon to investigate a site rumored to hold the Mermaid secret. They discover a hidden cave containing an underground construction plant. An Artificial Arm attacks the group, a threat Mirei recognizes intimately. After Mamori is incapacitated by a previous attack, Mirei activates her hidden powers but is overwhelmed. Mamori, determined to protect her friend, unleashes enhanced abilities and transforms into an enhanced arm. This transformation enables Mirei to defeat the Artificial Arm. The group escapes as the facility is destroyed. Meanwhile, another island detects the Valkyrie Effect from the battle and sends Momoka Sagara to Mermaid to investigate the incident.