This show is about Humans who used to live upon the ocean floor but there were a curious few who decided to leave and see the surface. Some stayed and lived there. As time went on, the surface people and the sea people became separated and usually had nothing to do with each other. Four of the sea world students named Hikari, Manaka, Chisaki, Kaname went to go start school in the surface because the school from the sea was abandoned. The sea world people were born with a thing called an Ena. It helps you breathe in the sea and makes you swim faster also allows them to live under water. One of four childhood friends (hikari) from Shioshishio , He has a short temper and usually scolds Manaka for her mistakes. Despite this, he has deep feelings for her, yet believes she is in love with Tsumugu. He is the son of Shioshishio's Chief Priest who serves the Sea God. Manaka also has deep feelings for hikari but doesn't know. Chisaki also thinks she has feelings for Tsumugu. At first, he hates all people from the surface, but after learning about the relationships between the land and sea humans (through Akari and Itaru), he gradually understands that there is no difference between the people from the surface and the sea.He goes into hibernation shortly after saving Akari during the Ofunehiki festival because manaka sacrificed herself to the god of the sea and stayed there until hikari broke the protection from the stone she was on. After the 5-year time skip, Hikari reappears during a Tomoebi without any signs of aging, making him the first person to do so. He rejoins Mihama Middle School as Miuna and Sayu's classmate and lives in the Shiodome home with his sister. while chiskai didn't hibernate and stay on the land with Tsumugu .They both also caught feelings for each other while they were on land and they both got together after she found out that manaka has feelings for hikari. Kaname had for feelings for chisaki but found out she didn't like him so then Sayu confronted Kaname that she had feelings for him and he started looking towards after her. In the last scene, Manaka and Hikari acknowledge each other's feelings and start a relationship, looking towards the future together.