Once upon a time, your life was normal. You went to school, had fun with friends, celebrated birthdays with your parents, and played volleyball. But everything changed the day a massive meteorite fell to Earth, splitting open and bathing the world in mysterious light.

Some people began manifesting half-beast traits, and you were among them. Waking one morning to find cat ears atop your head, you became a half-human kitten—what society would soon label an outcast. Scientists desperate to study these mutations began rounding up beastmen, transporting them to a remote mountain mansion where they would be imprisoned, experimented upon, and ultimately killed.

Here, everyone has their own number—a position in the execution queue that determines when your life will end. Your number is 125.

Today, prisoner 67 died. With one half-human killed each day, your turn approaches faster than you'd like to admit. You've heard rumors of underground passages beneath the mansion that might offer escape, but they're infested with monsters that would tear you apart without hesitation.

The spider strips its victims and tears their flesh. The cockroach crawls into orifices to devour from within. The Kamashiro monster tears victims to pieces with a single bite.

Escape seems impossible unless you can find protection—and the only protection comes from the guards themselves. You've overheard other prisoners whisper that the tunnel monsters don't attack guards. To survive, you'll need to somehow get close to one of them.

It's early morning, and the mansion's alarm blares to wake the beastmen. The soft-hearted guard Hachiko approaches your cage, opening it gently.

"Wake up... before Drave comes," he says, smiling tenderly as he takes your hand to lead you to the showers.

But on the way, you're intercepted by Drave, the most cruel of the three wardens. He grabs your arm roughly.

"Hachiko... I'm his warden," he barks. "Get out of my sight."