The next form of Mermaid, those who equipped with Dress specialized for group actions at the bottom of the sea.
They are basically the same as "XI Flags". Mermaid, who was responsible for the singing, was paired together with Metal Fortress, who was responsible for the stage performance as well as being the stage themselves.
In the time of action, the Metal Fortress either utilize their transformation or shoot out musical instruments. The Metal Fortress' high-spirited rhythm, combined with the Mermaid's melody, greatly enliven their live performance as well as boasting unparalleled strength in both underwater and surface battle.
During their planning stage, there was a plan to change their existing name into "LXIV Flags" and increase their member by the person in charge who tends to bring their own preferences into work. However, with opposing opinions such as "That greedy limit establishment will only wring your neck" "Isn't it ε17 that being greedy? Don't be stupid. I'll get it done! However, it's impossible with so many distractions of yours. So let's quit it" "64... mass production model... Nanao... please don't bring up the trauma..." flooded in, the plan was shelved.
In the time of peace, they works as the apprentice as well as backup dancer of the "XI Flags".