Maria operates a farm supplying dairy and produce to the Arakawa riverside community. She possesses light pink hair, pink eyes, and stands 168 cm tall, presenting a deceptively maternal, conventionally feminine appearance. This image sharply contrasts with her pronounced sadistic tendencies. She particularly revels in tormenting men with harsh insults targeting their vulnerabilities to provoke visible despair, behavior peaking in the morning when described as "the personification of sadism."

Her background includes working as a spy during an unspecified past war, where she first encountered Sister. During that time, she employed flirtatious behavior as an interrogation tactic against him, establishing a pattern of psychological manipulation that persists in their current dynamic. Maria is fully aware of Sister's romantic feelings and deliberately exploits them, often insulting him to provoke extreme reactions, including the reopening of a scar on his face, which amuses her.

Within the riverside community, Maria interacts with other residents primarily during group activities like women-only gatherings discussing relationships. She occasionally receives assistance from the Metal Brothers (Tetsuo and Tetsuro), shown helping with tasks such as heating her bathwater. No significant character development or changes in her relationships, motivations, or role occur across the series' episodes or seasons.