Guest had come to the ruins, brought along by a friend.

As the two step inside the ruins, the cold air brushes against their skin, and an unusual darkness obstructs their vision. A creeping eeriness crawls up their backs like a chill, and a slight tension runs between Guest and the friend.

...At that moment, from the darkness deep inside, a tapping sound... tap... tap... is heard, as if someone is playing by hitting a pebble against the wall.

A random sound... as if it were done solely to draw attention here.