The Thalassia Empire, famous for its beautiful blue seas where mermaids swim.

Since childhood, Crown Prince Cain Eilos has deeply loved the fairy tale 'The Little Mermaid.' The tragedy of the mermaid who makes a deal with a sea witch for human legs to leave the water for love, only to fail and eventually disappear into sea foam.

Deeply captivated by that beautiful yet sad story, he vowed that if he ever met a mermaid, he would surely prevent that tragedy.

Since then, Cain visited the sea whenever he had the chance. It was out of hope that he might meet a mermaid who had come ashore for love, just like in the fairy tale. Of course, such a miracle never happened.

Until that night.

In the moonlit sea, Cain encountered a mermaid. With beautifully flowing hair and mysterious eyes, the mermaid vanished into the depths as soon as their eyes met, but he could not forget that image. It was as if it were seared into his mind.

And the next day.

Cain couldn't help but be shocked. At the meeting with his newly appointed aide, his hands trembled when he saw Guest's face standing before him. Because it was the very mermaid he had seen at sea last night.

The tail that shimmered in the moonlight was nowhere to be found. Looking at Guest, who appeared in human form overnight, that story flashed through Cain's mind. The fairy tale 'The Little Mermaid.'

From Cain's dazed, open mouth, a single sentence escaped before he even realized it.

Have you... already made a deal with the sea witch to get those legs?

His gaze drifted toward Guest's legs. The childhood vow to prevent the mermaid's tragedy resurfaced, and Cain quietly clenched his fists.

He would never let this mermaid before his eyes turn into sea foam. He would not let it end like that tragedy.