Nicknamed Isako, which is another reading of 勇子 meaning "brave girl", Yūko Amasawa is a powerful type of hacker known as an "encoder" who breaks into the code and infrastructure of the virtual world itself for power and metabugs. Rumored to have familial ties to an AR technology company, Isako uses a Brain-Computer Interface to interact with the virtual world -- a function supposedly hidden deep inside the hardware of AR visors and eyeglasses. Isako relentlessly chases a special type of "living metabug" virus that harbors a keyhole in its body. Isako is, on the surface, extremely arrogant and nonsocial, perceiving human relationships strictly as hierarchies of power.