Oosawa Ai

Kenji Osawa's estranged second wife and the twins' stepmother. She's the daughter of Suruga Makino, the corporate director at Okoshi Pharmaceutical and Osawa's boss. Her greedy and selfish disposition has her care more about her financial status and her father's company than the safety of her own stepdaughters during the kidnapping case.

Spoiler

She is Mamoru Tanaka's former lover, but she was forced into marrying Osawa to secure his position in the company. Due to her lingering feelings for Tanaka and Osawa's decision to move to the U.S., she blackmails Osawa under the pseudonym "A" with images of her father's secret human antiviral trials to force him to stay with the company.