Mermaid Princess Athena makes a deal with her father to let her stay in the human world and pick out her own husband. But she must also come back with an heir. And so, she meets Kazune Kujyou, her true love.

Kenshin and Kaoru have been best friends since kindergarten. They're in love and share a night of passion. However, the next day Kenshin is nowhere to be found and Kaoru is left alone to deal with the aftermath of their night. Five years later he shows up at her doorstep in a drunken state, so she sends him home. When he returns to her the next morning he gets quite the surprise.

Karin isn't sure what to get Kazune for Valentine's Day.. But she's lucky to discover he already has an idea.