Akio Tademaru, uncle to Shiki Tademaru and biological father of Aya Tademaru, orchestrated a scheme targeting Shiki's mother, his sister-in-law. He arranged her rape by various kemono in pursuit of offspring inheriting the rare golden thread ability. This plan culminated in Shiki's birth. Akio later physically assaulted the young Shiki, rendering him unconscious to obscure the traumatic events, and manipulated him into believing their family had been attacked by external kemono threats.

Years later, after Shiki uncovered the truth of his origins and his mother's suffering, he confronted Akio. During this confrontation, Akio admitted his actions without remorse, explicitly stating his intent to exploit Shiki as a weapon. He further antagonized Shiki by callously dismissing the significance of his mother's ordeal. This culminated in Shiki executing Akio as retribution for years of manipulation and abuse. Akio's death served as a pivotal moment in Shiki's character development, resolving a central conflict rooted in familial betrayal.