Nagasumi Michishio is saved from drowning by a mermaid, Sun Seto.
Nagasumi discovers that Sun is actually a mermaid, putting him into a difficult situation.
Sun informs Nagasumi that they must marry to save Nagasumi's life due to mermaid laws.
Nagasumi meets Sun's powerful mermaid family and navigates their eccentric personalities.
The couple goes on their first date, deepening their relationship.
Suruga, a mermaid from a rival faction, makes her appearance causing tension.
Nagasumi fights off threats to Sun's safety from enemies of the Seto family.
Nagasumi is acknowledged as a member of the Seto family after overcoming various challenges.
