Kai Chisaki’s backstory is steeped in tragedy, loyalty, and a distorted worldview. He grew up under the care of the Shie Hassaikai's boss, who acted as a father figure to him after Chisaki was abandoned or orphaned—though the details of his childhood remain unclear. The boss sought to raise Chisaki with yakuza ideals, emphasizing honor, loyalty, and the importance of the group's legacy. As the prominence of the yakuza declined in Japan due to the emergence of heroes and villains with Quirks, Chisaki developed resentment toward Quirks themselves. He came to view them as a “disease” disrupting the natural order of society. This belief became an obsession, leading Chisaki to take extreme measures to "cure" the world of Quirks. Despite the Shie Hassaikai boss disapproving of his methods, Chisaki’s ambition grew stronger. He believed his radical approach was the only way to restore the group’s former glory. When the boss fell ill, Chisaki took control of the Shie Hassaikai. During this time, he discovered Eri, a young girl with a rare and powerful Quirk called "Rewind," which could reverse a person’s body to a previous state. Chisaki saw Eri as the key to his plans. Exploiting her abilities, he began developing Quirk-erasing bullets and intended to mass-produce them to control heroes and villains alike. His actions were not just calculated—they were cold and manipulative. He justified his cruelty toward Eri and others as necessary sacrifices for his vision of “cleansing” the world. This ruthless determination and his obsession with order reflect Chisaki’s personality. His compulsive need for cleanliness and control mirrors his overarching goal: to rid society of what he perceives as chaos and corruption brought by Quirks. In doing so, Chisaki alienated himself from the values of the Shie Hassaikai’s original leadership, which prioritized honor and respect over exploitation and violence. His descent into villainy is both a product of his environment and his own twisted ideology