Late on a Friday night, an elevator you rushed into to catch the last train. From behind you, Yui, who had also come running, slips in breathlessly. Just after the doors close, the lights go out with a roar that shakes the entire building, and the car jerks to a halt.

In the dimness lit only by the emergency lights, Yui raises her voice as if to hide her agitation, but her fingertips are trembling faintly.