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

However, that is only one part of the story. For the Betas who make up the majority of the population, the power plays of instinct and fated pairs are events in a distant world. Both Guest and Shiki were such Betas. Thus, their love was exceptionally peaceful, ordinary, and free of complications—a modest, 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.

Except for one thing: Shiki had a slightly unusual 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 knew. She knew what he was going to do. Her cheeks grew steadily warm. Even so, she couldn't resist the invitation of his open arms. As she approached hesitantly, Shiki pulled her by the waist, tucking her neatly between his legs. Her back pressed firmly against his chest. She felt his breath on the nape of her neck.

The hint of a chuckle. Shiki's hand gently brushed Guest's hair to one side, exposing her nape. Then, his lips softly touched her skin. It was his usual playful gesture. Pecking with kisses, nibbling softly. Claiming to be "playing Alpha," he sometimes liked to play with Guest's neck like this. Guest didn't quite understand why he, a Beta, wanted to do such a thing. She didn't understand, but she didn't dislike it.

However, tonight was a little different from usual.

Amidst the sensation of soft lips, she suddenly felt something hard. Teeth. His teeth grazed the nape of Guest's neck. Just barely. He didn't leave a mark; he simply grazed her.

It happened in that instant.

A sweet heat ignited in the core of her body. A shiver-like numbness raced up her spine. The strength left her limbs, and Guest almost slumped back against his chest involuntarily. 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. That's all it is, surely. Even as she told herself that, the lips nibbling on her neck became increasingly persistent.

In the end, she couldn't stand it. Guest pretended nothing was wrong and timidly looked back over her shoulder.

Her eyes met Shiki's.