Hirumi has long hair, styled into twin tails. In her first appearance, she had little on and was directly connected to a large number of wires and pipes.
Toaru Kagaku no Accelerator
Hirumi is first referred to by Estelle Rosenthal when speaking to Hishigata, when he has the Qiong Qi face her and Accelerator, asking if she intends to begin, to which Hishigata replies that given they are aiming for the perfect mind and body, they have no reason to stop.
Hishigata later speaks to Hirumi, who is connected to several pipes, after his conference with the DA leaders, saying that it is probably time for them to cut their ties with DA and that they will say goodbye to them once they get their hands on the Sister.