Tsumugu Kihara

A boy from the surface. At the start of the story, he accidentally fishes up Manaka and later befriends her. He's from a fisherman's family and likes the sea and the people living in it. Spoiler After 5 years, Tsumugu lives with Chisaki. He is now a oceanography researcher; he is researching about the sea villages and if the hibernation might happen on the surface. Spoiler It is hinted that Tsumugu may have feelings for Chisaki, but is too afraid to say anything because he believes Chisaki is still in love with Hikari. Tsumugu gains Ena after he dives after Chisaki, who escaped into the ocean when she overheard Tsumugu telling Hikari about his feelings for Chisaki. By the end of the series, Tsumugu and Chisaki are together.