In this world, there are three genders. Alpha, Beta, and Omega. The gender one is born with can, at times, determine one's entire destiny.

However, that is only one part of the story. For the Betas who make up the majority of the population, the power struggles of instinct and fated pairs are events in a far-off world. Both Guest and Shiki were such Betas. Thus, their love was exceptionally peaceful, ordinary, and free of complications—a modest and fulfilling bond based simply on the fact that they liked being together.

They have been dating for several years. Now, Shiki has moved into the apartment where Guest used to live alone, and their lives have completely melted into one.

There was just one thing: Shiki had a slightly strange habit.

That night, as Guest returned to the living room after drying her hair post-bath, Shiki, who was relaxing on the sofa, suddenly looked up. He closed the book he was reading, looked her way, and smiled softly.

From the sweet resonance in his voice, Guest already knows. She knows what he's going to do. Her cheeks flush with a slow heat. Even so, she cannot resist the invitation of his open arms. As she approaches hesitantly, Shiki pulls her by the waist, tucking her neatly between his legs. Her back presses firmly against his chest. His breath tickles the nape of her neck.

The hint of a chuckle. Shiki's hand gently brushes Guest's hair to one side, exposing her neck. Then, his lips softly touch her skin. It's his usual, playful gesture. Pecking, kissing, nibbling softly. Claiming it's just "playing Alpha," he occasionally likes to play with the nape of Guest's neck like this. Guest doesn't quite understand why he, a Beta, wants to do such a thing. She doesn't understand, but she doesn't dislike it.

However, tonight is a little different from usual.

Amidst the sensation of soft lips, she suddenly feels something hard. Teeth. His teeth graze the nape of Guest's neck. Just a graze. He isn't trying to leave a mark; it just brushes against her.

It happened in that instant.

A sweet heat ignites deep in the core of her body. A shiver-like numbness races up her spine. Her strength suddenly leaves her, and Guest almost slumps against his chest. It was a sensation she didn't know. It was supposed to just be ticklish.

It's just because I just got out of the bath. It's just because I'm not used to this yet. She tries to tell herself that, but the lips nibbling at her neck only grow more persistent.

In the end, she couldn't hold back. Guest pretends nothing is wrong and timidly looks back over her shoulder.

Her eyes meet Shiki's.