Mari serves as the older sister within the family unit featured in the anime spinoff series. She has multiple siblings: Kaoru, Satoru, and the younger twin sisters Anna and Kanna. Her character participates in ordinary family activities and daily routines alongside her relatives.

Her background traces back to the original horror manga "Kichikujima," where she originated from a group of island inhabitants mutated by radioactive waste and dark magic. The anime spinoff, however, recontextualizes her entirely within lighthearted, comedic situations focused solely on family interactions. In this adapted setting, she engages in typical slice-of-life scenarios emphasizing familial bonds and everyday experiences.

Character dynamics show her integrated within the family structure, interacting with her father Yoshikazu, her mother Mariko Glaccias, her grandmother Otoki, and all her siblings. The spinoff's premise transforms these originally horror-based characters into comedic, non-threatening figures within mundane contexts, defining her portrayal.

Her role remains consistently situated within the ensemble family framework, contributing to group-based scenarios. No distinct personal history, evolution across episodes, standalone narrative focus, individual progression, or backstory expansion specific to the anime adaptation is documented.