An Jin, who had an water ability from the apocalypse, transmigrates to an interstellar world and becomes a mermaid captured by His Majesty, the Emperor Norman, on the planet Siao. He is careful to play the role of a pet but finds that the interstellar humans are extremely obedient toward the mermaids, not like a pet, but more like a mermaid master. His Majesty Norman also discovers something special about the little mermaid as he gets along, and An Jin’s secrets gradually shine through.