"No... Yuzuru... It's going to break!!" Nagi, a "mermaid" who takes on a human body only during the breeding season, visits Ruri Island to be embraced by Kaito, the human who helped her when she was a child. Kaito, who has always been in love with her, continues to be kind to those in need even as he grows up. However, she is told that the mermaids during breeding season need to be embraced by the priest so that they don't turn back into humans... Yuzuru, the chief priest of the shrine, sucks her breast and loosens her vagina with his fingers and tongue. The body that remembers the climax becomes hot to the back. In order to be united with Kaito, I have no choice but to surrender myself as it is...!? 「だ…め…弓弦っ…壊れちゃう!!」蜜があふれる奥を激しく責められ、想いとは裏腹に何度もイかされて――。繁殖期の間だけ人間の身体になる“人魚”のナギは、子どもの頃に自分を助けてくれた人間・海斗に抱かれるため瑠璃島を訪れる。ずっと想い続けた海斗は成長しても困った人を助ける優しさは変わらず、男らしい力強さも加わってナギはますます惹かれていく。しかし繁殖期の人魚は、人間に戻らないよう宮司に抱かれる必要があると聞かされ…。神社の宮司・弓弦に胸を吸われ、ナカを指と舌でほぐされ、初めての快感に戸惑うナギ。絶頂を覚えた身体は奥まで熱くなってしまい――。海斗と結ばれるためにはこのまま身を委ねるしかないの…!?