Erii is a young Mushitsuki who controls a pack of White Swallowtail butterflies to manipulate electrics. She can gain access to all equipment that requires electrics to operate, and can even have visions by sending currents through any medium that conducts electrics. These proven to be very powerful abilities in the urban environment. She can also summon her White Swallowtail butterfly to shoot electric beams to paralyze opponents.

Her dream is to "know every secrets about the world." In Mushi-uta Bug Vol. 5, ch.18, She was discovered by Central SEPB, and Daisuke brought Arisu and Neiko to investigate. Arisu used her ability to "challenge" Daisuke and his company but Daisuke managed to break every obstacles. When she was discovered, her brain was about to burnout by uncontrollably accessing too much information, but she was too afraid to shut down her power. Daisuke did an unusual act, which was to spare her, and convinced her to shut down power with Arisu.

Erii was later sent to Eastern Central SEPB under the supervisor of Inuko. She slowly learned how to control her power and became a high ranked member in the intelligence section of Central SEPB.

Erii also made an appearance in the anime adaptation: