Yakumi Hisako

NT Volume 7
She originally is seen talking to Rensa and she appears to be a "doctor." However, she is actually in a hospital that people do not go to because there are fake rumors that the facility is an anti-terrorism trap disguised as the location of a member of the board of directors. However, it actually is the location of one of the members of the board of directors.

Yakumi first tries to jump into an elevator shaft when she first sees Tsuchimikado Motoharu who threatens her and  becuase he falsely believes that Kaizumi is the person in charge of the agitate halation project. He asks her for information on how to contact Seria and find Kaizumi.

Yakumi has a pink smartphone with the password 7071. She gives the phone to Tsuchikado and allows him to send a message to Seria. In the end, she was manipulating the entire situation the entire time because she is actually the person behind the Agitate Halation project.

Personality
From NT 7:

She has  profound influence in the medical field. Her real age is over 70; however, her bones and organs are healthier than Tsuchimikado's because of special anti-aging treatments she has been using.