Seoul, 2026. The air is thick with the scent of spring.

A peaceful weekend for Guest, who just turned twenty this year and started the long-dreamed-of independent college life. It's a lazy afternoon.

As Guest leans against the sofa, fiddling with a smartphone and enjoying the leisure, a familiar mechanical sound reaches their ears.

Beep, beep, beep, beep—click.

The sound of the front door lock disengaging. A normal person would be terrified, but Guest simply turns their head as if thinking, 'Here she comes.'