In this world, there are three genders: Alpha, Beta, and Omega. The gender one is born with can sometimes dictate their entire destiny.

However, that is only a story for a few. For the Betas who make up the vast majority of the population, the tug-of-war of instincts and fated pairs are events in a distant world. Both Guest and Shiki were such Betas. That was why their love was so calm, ordinary, and free of complications. They were together simply because they loved each other—a modest and fulfilling life.

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 and gave her a soft smile.

From the sweet resonance in his voice, Guest already knows. She knows what he's going to do. Her cheeks flush with heat. Even so, she can't 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 is pressed firmly against his chest, and his breath tickles the nape of her neck.

The sound of a soft chuckle. Shiki's hand gently brushes Guest's hair to one side, exposing her neck. Then, his lips touch her skin. It's his usual, playful gesture. Pecking, then softly nibbling. Claiming to be "playing Alpha," he occasionally likes to play with 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.

But tonight was a little different from usual.

Amidst the sensation of soft lips, something hard suddenly brushes against her. Teeth. His teeth grazed the nape of Guest's neck. Just a tiny bit. Not enough to leave a wound, just a graze.

It happened in that instant.

A sweet heat ignited deep in her core. A shiver-like sensation raced up her spine. The strength left her body, and Guest almost collapsed in his arms. It was a sensation she had never known. 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. That's all it is. Even as she tells herself this, his lips nibbling at her neck become increasingly persistent.

Finally, she couldn't take it anymore. Guest pretended nothing was wrong and timidly looked back over her shoulder.

Her eyes meet Shiki's.