Ai Demoto is a central character, closely bonded to protagonists Kadode Koyama and Ouran Nakagawa throughout high school and university. Her strongest connection is with Rin Hirama, her best friend and childhood companion since kindergarten.

Her family life is deeply affected by the "8.31 incident," an alien spacecraft appearance over Tokyo. Environmental pollution classified as "Line A" contaminated their Ota Ward residence, prompting her parents to relocate to government-provided special housing for financial aid. Ai chose to remain behind, taking on the responsibility of caring for her five younger brothers. The siblings live together in a relative's house near her school, ensuring her education continues uninterrupted and cementing her role as the family's primary caregiver.

Physically, Ai possesses a short, round stature, small eyes, and a distinctive look marked by prominent oversized glasses. She maintains a generally cheerful personality, finding purpose in her busy household life with her brothers. Despite the societal and political tensions fueled by the ongoing alien presence and cold war—dividing factions into "warctopuses" (advocating alien elimination) and "peacesquids" (advocating negotiation)—Ai largely ignores these conflicts. Her focus remains firmly on her familial duties and personal relationships, not the broader geopolitical events.

Throughout the narrative, Ai consistently prioritizes her immediate personal connections and domestic responsibilities over external societal pressures, a defining characteristic. This perspective makes her a stabilizing figure grounded in everyday realities against a backdrop of wider uncertainty. Her background, displacement due to environmental contamination, and current caregiving role provide essential context for her motivations and interactions within the group.