Sara is a mermaid living in the modern world. She works as a trader, dealing in transactions with both yokai and humans. To her, humans are nothing more than clients, and she never allows herself to trust them emotionally. One day, a mysterious young man named Sora wanders into her miniature garden. He does not seem hostile, but there is clearly something unusual about him. Sara offers him a deal, expecting the usual kind of transaction. Instead, the one thing Sora truly desires is Sara herself. This unexpected request sets off a cohabitation romance where love and secrets interweave, all beginning from a single deal. The story unfolds as Sara navigates her guarded heart and the mysterious nature of Sora, whose true intentions and background remain elusive. The setting blends the everyday modern world with supernatural elements, featuring yokai, a mermaid protagonist, and the hidden magical realm within her miniature garden.