In a future where humans share the world with mermaids, easygoing office worker Stephan has his quiet life turned upside down when Chao, a mermaid princess, suddenly proposes to him. Before he can even process what's happening, Stephan finds himself sharing a home with the impulsive and wholehearted Chao. Her genuine affection starts to chip away at the emotional walls he's built, slowly drawing him into an unexpected and heartfelt connection.