Kusumoto has an aged appearance and dresses formally.
Kusumoto cares deeply for her son, and never truly moved on from his suicide attempt.
In 2008, her son attempted to commit suicide by jumping off the roof of his school due to the bullying he endured, and was rendered comatose as a result. The bully, Shinya Kawai, begged for forgiveness afterward and Kusumoto visited her son every night, with Yoko Sawa being the only classmate of Mitsuru who would visit. Yu Kitakata, the teacher whose negligence allowed the suicide attempt to happen, contacted Kusumoto and offered to kill Kawai to atone for his mistake, but visited Kamurocho to meet Kawai before making a decision. Kusumoto was approached by Kawai, who mistook her as a woman looking for men to date. Her son's bully forgetting both his guilt and who she was angered Kusumoto, and she took up Kitakata's offer. Kawai was abducted by Kitakata's contacts, and Kusumoto stabbed him in the chest with Kitakata as the sole witness.
Kusumoto became the Vice Minister of Health in 2021 following the arrest of her predecessor, Kaoru Ichinose, and his successors being unable to maintain control in the ensuing chaos. She also had Mitsuru transferred to Touto University Hospital in hopes of a potentially more viable recovery.
Lost Judgment: 2021-2022
Kusumoto is a popular government member in part due to the tragedy surrounding Mitsuru. In the government itself, however, she is someone who poses a danger to the status quo due to the amount of leverage she has, to a point where even the Prime Minister has trouble with her. She is the main obstacle preventing her political rivals from using the ¥160,000,000,000,000 taxpayer-funded pension, which is under the Ministry of Health's jurisdiction. Because of this, Hidemi Bando aims to find a weakness in her.
Following Sawa's murder, Kusumoto receives a phone call from Kitakata, who now goes by the name Jin Kuwana. Though the conversation appears to be Kuwana updating Kusumoto on current events, its real purpose is to see if her phone is wiretapped by Public Security, which is confirmed shortly. After the call, Bando enters the room to ask her about Kawai, suspecting she played a part in his disappearance.
A few days later, outside the hospital, Takayuki Yagami and Fumiya Sugiura come into contact with Kusumoto in a taxi ride where they inform her Public Security is monitoring her, and request she turn herself in for the damage caused by Kuwana's murder conspiracy. Though she does not want to do so, Yagami gives her a phone to call him if she decides otherwise.
Being indirectly responsible for the death of the only person who would visit Mitsuru causes her to feel guilty, and she chooses to turn herself in to allow Sawa's killer to face justice. She calls Bando to Mitsuru's room to inform him of this, but before she can commit to her decision, Mitsuru wakes up, overwhelming her with relief. Bando convinces her to avoid turning herself in by telling her Mitsuru will be branded the child of a murderer if she does not change course. Kusumoto relents, and informs Public Security of Kuwana's link to the Kurokawa Academy graduates. She also has Kazuki Soma pass a message to Yagami: Do not mention her name at the retrial of Akihiro Ehara. Around this time, she receives a letter with a request from Kuwana, asking her to allow him to contact Yagami through her phone.
After Ehara's trial in 2022, Kuwana calls Kusumoto's phone. He states he does not harbor a grudge against her and is standing next to Kawai's preserved body, and that he is allowing Public Security to trace his location. Later in the day, Kuwana uploads an image of Kawai's body, and Kusumoto has a change of heart after seeing the pain on his face preserved. She meets Kuwana at the warehouse he hid the corpse, and tells him of her decision, adding that she wants to free him of his burden. Before going with the police, she calls Mitsuru to inform him of her absence, to which he says he will support her when she returns. After she is arrested for Kawai's murder, she fully cooperates with the investigation.