Mari Aragaki is the mother of Jotaro Aragaki and grandmother of Rei Aragaki, sharing a household with both. Her appearance features pale skin and asymmetrical short pale pink hair swept to the right. She dresses in a flashy, noticeable style, typically wearing pale yellow sunglasses, large earrings, a red coat over a teal shirt, black gloves, black leggings, gold shoes, and a purple patterned scarf.

Mari displays a laid-back personality and worldly wisdom. Though deeply caring for her son and granddaughter, she maintains some personal distance. Her past is largely undefined, but she possesses extensive international connections, exemplified by gifting Rei a rare South American bird. She owns and operates Snack Mary, a bar in Ikebukuro. Her behavior includes reckless driving, with implications she modified her car with rocket engines, hinting at hidden depths beneath her ordinary exterior.

The surname "Aragaki" combines the characters for "laid waste, rough, rude, wild" (荒) and "hedge, fence" (垣).