Kumoshichi began life as a human called Shikiji fifteen years before the main story. During Ryūdō Yukiatsu's reckless period after returning from the Other World, Kumoshichi formed a friendship with him. He was romantically involved with Oshino, who deeply cared for him and desired marriage. Alarmed by Yukiatsu's self-destructive spiral—marked by brawling, gambling, and sexually harassing Oshino—Kumoshichi deliberately provoked Yukiatsu, aiming to force a confrontation over his behavior. This clash turned violent, resulting in Yukiatsu killing Kumoshichi while defending himself.

Kumoshichi's death inflicted severe psychological trauma on Yukiatsu, causing him to completely suppress the memory. Subconsciously, Yukiatsu manifested a Yoi—a supernatural entity from another world—in Kumoshichi's exact likeness. This manifested entity, perceived as Kumoshichi, became Yukiatsu's constant companion, shadowing him everywhere and frequently offering advice. Only Yukiatsu could see this entity, making him appear to talk to himself. Atl, an Aztec girl, proved an exception, perceiving the Kumoshichi entity and correctly identifying its non-human nature.

The Kumoshichi entity functioned as a coping mechanism for Yukiatsu's buried guilt and trauma, embodying his unresolved feelings about the death. It retained the original Kumoshichi's personality and memories, acting as a guide and confidant. This entity persisted until a critical event involving Atl's dragon-horse, Quetzl (also called Yukiwa). When Quetzl became uncontrollably dangerous, the Kumoshichi entity merged with it to pacify the creature. This fusion transformed Quetzl into a talking horse, housing Kumoshichi's consciousness. After this merger, Kumoshichi ceased appearing in human form, existing solely within the transformed Quetzl.