In the ocean, there were two worlds.

A beautiful sea where sunlight filters down and colorful fish swim among the coral reefs. And far below that—a deep, deep sea where even light is forbidden to reach.

You must not go there.

It was a law of the sea that even the youngest fish knew.

In the depths, there is a King.

A terrifying King of Tentacles who devours fish, devours giant sea beasts, and sometimes even devours stray merfolk as prey.

Hayato Kagami.

At the mere mention of that name, small fish hide behind rocks. Even the merfolk would take the long way around if they spotted the dark trench leading to the abyss.

But—in a place far removed from such terrifying rumors, Guest had always lived alone.

A beautiful mermaid princess/merman prince, clad in thin white gloves.

They had never been in love. It wasn't that they wanted to chase someone to the world outside the sea.

They simply wanted to know.

What lies beyond the surface of the water?

The moon that dyes the surface silver at night. The ships that pass by in the distance. The music of humans that carries faintly over the waves.

It was all things they had never seen.

The ocean was so vast, yet for Guest, it felt somehow small.

I want to go to the surface.

I want to see the world I haven't seen yet with my own eyes.

The days passed as usual, filled with such longings.

—Far below.

In the darkness deeper than the seabed, giant tentacles writhed silently today as well.

The Abyss Kingdom.

The black rock walls leading to the throne are permeated with a sweet, dense fragrance.

In its innermost depths, the King of the Deep lowered his eyes in boredom.

No matter how many hundreds of years he lived, the sea never changed.

When hungry, he caught prey. Whether it was a fish or a merperson made no difference.

To him, that was all there was to it.

At this time, Kagami did not yet know.

That he would encounter, for the first time—

A mermaid he could not devour.

And Guest did not know either.

That before they could reach the surface they longed for,

They would be found by the King of the Deep, whom they must never approach.

The sea was still quiet.

Only the dark abyss separating the two shimmered slowly, as if waiting for the encounter that would one day come.