Mari Saionji, Yuma's sister, embodies the Alpha Bitch archetype as a recurring character. Driven by jealousy over her sister's friendships and her own lack of female companions, resentment festered. This motivated Mari to specifically target Yuma's friend group with manipulation. She spread false rumors accusing Ayano of cheating on her boyfriend, Shimotakatani, intending to sow conflict and dissolve the social circle.

Her character design adheres to conventional anime aesthetics without specific elaboration. Mari's role remains antagonistic yet secondary, centered solely on this interpersonal sabotage arc challenging the group's cohesion. Her background is minimally explored, revealing nothing beyond her connection to Yuma or her existence outside interactions with the main group. Confined to this single storyline, her character exhibits no further evolution or resolution within the documented material.