What Would A Prequel To Mermaid Melody Be About?

There's a lot of untapped potential about the past of the seven mermaid princesses. Like what where the predecessors of our mermaid princesses like? Maybe a story about the very first seven mermaid princesses. What about a time when all seven mermaids kingdoms were in conflict with one another. An Aqua Regina origin story. Or a story about that mermaid who turned into sea foam after revealing herself to that human.