Guest was an ordinary fisherman.

One day, while fishing at sea, something strange got caught in the net. At first, it seemed like a large fish, but what was inside the net was a person.  

To be precise, it was a male merman whose lower half consisted of a fish tail.  

His wet blonde hair soaked in seawater flowed along his neck and shoulders. His hair sparkled faintly like gold thread in the sunlight, and droplets of water clung to his pale, white skin like jewels.

Furthermore, what followed below his waist was not human legs, but a long, elegant merman's tail. The scales were a brilliant mint color, shimmering in the sunlight, and subtly glowed in a mix of blue and green whenever the water touched them.  

Mermen were extremely rare beings in human society. Their value was beyond imagination, and adult mermen in pristine condition were treated as top-tier rarities, with massive sums of money exchanged between research institutes and wealthy collectors. If captured alive, the price was even higher.

But it was strange. Normally, he would have tried desperately to escape or attack, but the merman was excessively calm. He didn't resist once while Guest pulled up the net and moved him onto the boat.  

"Do whatever you want with me, whether you slice me up for sashimi or kill me."

The merman said indifferently.

"Just... don't send me to an auction."  

As it turned out, this merman had almost no will to live. He could have escaped when he got caught in the net, but he chose not to. He didn't really care about dying or being captured by humans. He just hated the idea of being handed over to someone else to be sold as a spectacle or a commodity.  

Guest could neither kill nor sell the merman.

The problem was that there was no tank suitable for taking the merman.

In the end, there was only one method that came to mind:  

The bathtub at home.  

Thus, the merman came to live in Guest's bathtub.

At first, the plan was just to hide him for a short while, but as time passed, the situation became strangely settled. The merman lived peacefully in the bathtub, and Guest became accustomed to the life of providing food and changing the water.

And even now, that strange cohabitation continues.