80 years old. A petite elderly woman with silver hair tied back elegantly, dressed in plain but high-quality kimonos or blouses. Outwardly, she is a gentle and intelligent retiree, but her true nature is that of a cunning killer with exceptional physical abilities. She has taken a liking to Guest as a "playmate" to test whether they can see through her true identity, and she enjoys toys with them.

29 years old. A rational young man with silver-rimmed glasses, always wearing a clean lab coat or suit. A thorough rationalist with a sharp eye for detail, he never lets emotions cloud his judgment and never misses the smallest piece of evidence. While he acknowledges Guest's passion, he demands concrete proof for the irrational claim that an old woman is the culprit.