Kumi is a woman of average height with a slender build and pale skin. She has long, soft pastel pink hair that falls past her waist, though she often ties it up in a bun for practicality. Her eyes are magenta, and she has six small, dark markings on her forehead, resembling the additional eyes of a spider, a subtle nod to her Arachne heritage.

She typically dresses in traditional Japanese clothing and has been seen wearing various garments such as kimonos, yukatas, and jinbei. Her footwear often consists of azumasun (traditional Japanese wooden sandals) worn with socks, although she is occasionally seen walking barefoot.

In her Kemono form, Kumi undergoes a more dramatic transformation. Her eyes become completely black, lacking irises and pupils. Two spider-like limbs extend from each side of her torso, and a large, fur-covered structure resembling a spider’s abdomen emerges from her back, highlighting her Arachne lineage.

Kumi is portrayed as a gentle and selfless woman who places the well-being of her children above all else. Following the loss of her partner, she continued to raise Shiki with unwavering love and care, despite the emotional burden she carried. Her deep concern for her son’s future eventually led her to seek outside assistance, which tragically resulted in her exploitation by Akio and subjection to inhumane experiments.

Even under extreme suffering, Kumi never abandoned her role as a mother. Her empathy extended not only to Shiki and Aya, but also to the other children born from the experiments, toward whom she felt a quiet, maternal affection. When she is finally reunited with her children, Kumi welcomes them with warmth and tenderness, demonstrating that her compassion and maternal instincts endured despite the torment she had faced.

Kumi lived a quiet life in the forests of Kinshi-Go, located in Gunma Prefecture. One day, she was discovered by the Tademaru brothers. The eldest of the two fell in love with her, and the two eventually started a family together. Before the birth of their child, however, he died in an accident within the forest, leaving Kumi heartbroken and alone to raise their son, Shiki.

After Shiki was born, Kumi became concerned when he caught the flu, a human illness for which there were no available treatments in the Kemono world. Seeking help, she turned to her brother-in-law, Akio Tademaru, who brought the child to a hospital for medical care. Witnessing the human world’s capacity to provide what she could not, Kumi began to wish for Shiki to live a human life, one beyond her ability to offer as a Kemono.

In response, Akio presented her with a proposition. He offered her a job that involved using her Arachne abilities to generate income by participating in a project aimed at creating a hybrid capable of producing thread with healing properties. This involved engaging with various Kemono and non-human entities in experimental reproduction. Believing this would secure a better future for Shiki, Kumi reluctantly agreed.

Akio subjected her to numerous experiments, using Kumi as the maternal base for a long series of failed attempts to create the ideal hybrid. Over time, the strain from repeated trials caused Kumi’s health to deteriorate, but Akio persisted. His experiments ultimately succeeded with the birth of Aya Tademaru, a child with unique abilities.

Following Aya’s birth, Kumi’s body left in a comatose state due to the toll of the experiments was eventually healed by her daughter’s powers. However, Akio later concealed Kumi’s body in a water-filled chamber, wrapping her in a cocoon made by Aya and hiding it with the scent of skunk cabbage flowers to mask her presence.

As an Arachne-type Kemono, Kumi possesses several abilities typical of her species: