Atsuko Ōyama possesses black hair and belongs to the Ōyama family, sharing a household with her father, mother Akiko Ōyama, and sister Hana Ōyama. Her father discovered a stray tiger-striped cat during a Christmas Eve snowfall, leading the family to adopt it. Named Mi-kun, this cat integrates into their daily routines, with Atsuko's experiences reflecting the family's interactions marked by both joyful moments and challenges. She appears in the 1999 two-episode OVA adaptation, fulfilling her established role within this family dynamic.