Ai's grandmother inhabits the eternal twilight realm alongside Ai, her title reflecting cultural deference rather than confirmed kinship. Shrouded in mystery, she manifests only as a silhouette behind a shōji door, her obscured form provoking visceral terror—exemplified by Hotaru’s panicked flight—and hinting at a spectral nature evocative of the onibaba, demonic hags from folklore.

Confined to her chamber, she occupies herself with endlessly spinning a wheel, halting only to aid Ai by readying her nagajuban or announcing clients. Her awareness transcends physical boundaries, detecting intruders near the house and intuiting Ai’s unspoken emotions. She wields authority over the twilight realm’s thresholds, exemplified when bargaining passage for Hajime Shibata in exchange for an unnamed task.

Seldom engaging with others beyond Ai, her sparse dialogue reveals a detached vigilance. She commands Hajime, rebukes Kikuri’s meddling, dismisses Hotaru’s overture, and conveys Ai’s thanks to allies. Though reserved, her words occasionally betray concern for Ai’s welfare or oblique insights into ongoing cases.

Her disappearance during Ai’s third-season hiatus aligns with Yuzuki Mikage’s associate Akie temporarily assuming analogous duties—a role Akie fulfills despite prior damnation. This parallel implies Ai’s grandmother may similarly exist as a condemned soul co-opted by hell’s hierarchy to mentor the Hell Girl, her presence waxing and waning with Ai’s active service.

Her origins remain obscured, though supernatural traits—agelessness, confinement to twilight, and freedom from mortal needs—hint at binding through Ai’s infernal pact. The ceaseless spinning wheel she tends may allegorize vengeance’s cyclical machinery or fate’s entanglement, though its explicit purpose remains undefined.