Prayer of the seven seas is the 67 episode of the series and the 15 episode of season Pure.
Lucia, Hanon, and Rina head for Antarctica after recent events there worry Karen. Something is causing an enormous iceberg to melt, which can create a tsunami across the whole globe. The mermaid princesses must use all their strength to prevent global disaster by Mikeru.
Subaru was researching on why the ice in the Antarctic is melting. He went out side and saw Karen staring at the Legendary Glaicer. Subaru told her not to worry. Suddenly the ice was shaking violently and Karen knew it was starting that the Legendary Glaicer is melting. In a store, Lucia nad Hanon are trying out dresses and Rina came out wearing an outfit that she felt was not her but Lucia and Hanon disagree saying that it suits her. They both tease her a bit making Rina turn red and shouting that she will never wear it again. Lucia and Hanon saw Hippo and ask why is he here and why is he not wearing any clothes. The pegiun turned around and say peg peg. Hanon then say that is not Hippo. The girls and the pegiun went back to the Pearl Piari to discuss about something. The pegiun was the girls met was Pipi. Pipi told eveyone that she was sent by Karen and that she was in trouble. The girls, Hippo and Pipi went to the Antartic Ocean and is met by Karen who thank them for coming. Karen then apologized for not letting the girls rest after traveling all the way to the Antartic but the girls insisted. Karen then showed them the Legendary Glaicer and that it was begining to melt. The ice shook again and the the girls found Subaru stuck on the ice. Karen helped him and as he was about to introduce himself, he slip and got his foot stuck again. Karen was embaress that he was a bit clumsy. She then help him again and Subaru ask the girls where their from because of Karen telling Subaru that they are part of her research group. Lucia and Hanon both said here and point at opposite directions causing Subaru to become speachless and Karen to be shocked. The girls tried again and say there but again put at opposite direction causing Rina to take them away from Subaru. Karen went after them after Subaru told that he will see her again. Somewhere on the ice, Karen was scolding Lucia and Hanon for what if Subaru was becoming suspious. Hanon then asked if Subaru likes her which to Karen's suprise for the sudden question and struggle but couldn't give an anwers. Lucia then asked what do Karen feel for him which Karen anwsered. As the girls smiled for Karen's love life the ice shook again and created a big crack. Lucia then fall and Hanon began to panick. Lucia fall into the water and found out there was a machine that pumping hot water to melt the ice and that it was the Black beauty sisters who are the cause of it. Lucia was then captured in the machine by the current. Karen, Hanon, Rina, Hippo, and Pipi were looking for Lucia in the waters but could'nt find her. Karen then started to blame herself for what had happened to Lucia. Rina slap Karen and told her not to think like that and Hanon told her that they, mermaid princesses must also do their best for each other. Karen then told Pipi to give a message to the other mermaid princesses. Subaru was captured by the Black beauty sisters and he was hypontize to increase the heat for the machine to make the ice melt faster. Lucia awake to find herself in a cage and was forced to watch what was going on. Karen, Hanon, and Rina transfrom to try to stop the cause of the melting of the Legendary Glacier but were stoped by the black beauty sisters. Sheshe ordered Subaru to fight Karen which he cannot listen to anything Karen says. Rina knocked him out and told Karen to take hime to a safe place.