The Mysterious Man confronts Kun during a tantrum in the family garden, proclaiming himself the displaced "prince" of the house. He voices resentment over losing his status and the parents' attention after Kun's birth, complaints mirroring Kun's own feelings towards his new sister Mirai. Kun identifies the figure as Yukko, the family dog, upon noticing the man's tail. Detaching this tail and attaching it to himself temporarily grants Kun dog-like features – a tail, whiskers, and ears – enabling him to behave like a dog. The Mysterious Man's existence stems directly from Yukko's life as the family pet before Kun arrived. His role illustrates themes of displacement and jealousy within the family, vocalizing Yukko's perspective to help Kun recognize how attention shifts with new members. He later assists Kun and Mirai during the Hinamatsuri incident by helping store the holiday dolls. The tail functions as a transformative object, facilitating shifts between human and animal states for both the Mysterious Man and Kun. His presence is confined to Kun's garden experiences, serving specifically to facilitate Kun's understanding of family dynamics.