The show builds itself around a simple, devastating question: what do you choose when staying together means losing everything else? Lucia's love for Kaito isn't background noise to the adventure, it's the weight pressing down on every decision, every transformation, every moment she could be home instead of human. The Pure season doesn't soften this. It deepens it, forces her to watch the people she loves move on while she's stuck between two worlds that both demand sacrifice. Michel's arrival isn't just another villain. He's the show asking if love can survive when the fundamental choice, human or mermaid, stay or leave, him or her entire civilization, stops having a good answer. This is a mahou shoujo that understands what it costs to be devoted to someone, and never pretends that understanding makes the choice easier.

Peace settles over the ocean after the final battle against Gaito, but Sara has given her life to stay by his side, leaving the sea world with only six mermaid princesses. Caren, Noel and Coco have gone home to their kingdoms, and it seems time for Lucia, Hanon and Rina to follow. Mitsuki Tarou is leaving for Germany and Kaito is bound for Hawaii, which leaves Lucia crushed. Then Kaito is lost at sea, and a strange angel named Michel appears, wanting the mermaids to join him. There is some hope as well: Sara's spirit tells Lucia about her successor, a young mermaid named Seira. The sequel is a musical magical girl adventure that mixes fantasy, comedy and romance.