TV-Series
Description
Kō Satomi emerges as the central antagonist in Lostorage incited WIXOSS, adopting the alias "Bookmaker" to manipulate Selector battles. He appears as a man in his early to mid-twenties, characterized by neck-length black hair swept to the left and piercing blue eyes. His personality is calculating and sadistic, finding distinct pleasure in observing Selectors' suffering and occasionally documenting their despair. He openly declares human memories worthless garbage. Satomi's fascination with these battles stems from a desire to witness the volatile "chemical reactions" they ignite among participants.

Originally a LRIG, Satomi fought numerous battles partnered with the human Kō Satomi, defeating Aya Narumi—Shou Narumi's younger sister. Growing bored with conventional conflict, he sought greater thrills. He manipulated his own Selector into losing all coins, seizing the human's body permanently. Finding human existence ultimately unfulfilling, he craved life-or-death stakes again. This drove him to devise a plan to become a Selector and control all battles, emulating Mayu's earlier role. Allying with the LRIG of the Beginning, he acquired Carnival as his LRIG and established a network of Selectors by spreading rumors about the Bookmaker.

During Lostorage incited WIXOSS, Satomi orchestrates key manipulations:
- He forces contracts onto Suzuko Homura and Hanna Mikage by exploiting their vulnerabilities.
- He grooms Chinatsu Morikawa to embody his ideals of strength, intending to corrupt and ultimately destroy her. He engineers a lethal battle between Rio Koshiba and Shohei Shirai—both reduced to one coin—to punish Chinatsu for hesitation.
- He battles Shou Narumi, revealing his past as a LRIG and his goal of revenge against humans who exploit LRIGs. After defeating Shou, he taunts Shou's LRIG (Aya) about his plans.
- Confronting Kiyoi Mizushima, he identifies her as a fellow LRIG from past battles, claiming their similarities make her his "doppelgänger." He attempts to break her resolve by referencing her history of causing despair.

Suzuko Homura defeats Satomi in the climax, destroying his original soul. However, his LRIG Carnival survives, taking control of his body and continuing his legacy in Lostorage conflated WIXOSS. Under Carnival's influence, Satomi's physical form persists as an antagonist, devoid of his consciousness. Carnival utilizes his identity to escalate new Selector battles, introducing a "Key" card mechanic allowing Selectors to become LRIGs and wager captured LRIGs as higher stakes. This perpetuates Satomi's initial vision of intensified suffering, with Carnival manipulating battles for entertainment from within his form.

Satomi's backstory as a LRIG who despised being a tool for human wishes fuels his nihilistic philosophy. He views memories as burdens hindering true strength, a belief solidified witnessing human selfishness during his time as a LRIG. His ultimate plan—creating an "unbound" champion only to later destroy it—epitomizes his desire to expose the futility of human emotions and wishes.