Coveted for their ability to heal any ailment when their flesh is consumed, doctor mermaids are often fished up and sold at auctions. One particular mermaid captured for this purpose was purchased by Fuboku Mouki, one of the oldest and richest tycoons in the world, for 11 trillion yen. But rather than killing and eating the mermaid to cure his illnesses, Mouki decides to keep her safe in his estate property until the mermaid fishing season is over. Intrigued, the mermaid is determined to repay his kindness while also uncovering the reason why such a sickly old man would spare her life. [Written by MAL Rewrite]