Zest Do Bernard serves as knight commander for the Seven Light Faith, an organization supporting the protagonists' revolution. A member of the Byuma race, he possesses animal ears, a tail, an eye patch, facial hair, and a scar. Bernard is a widowed single father whose wife died in an epidemic; this tragedy drove him to knighthood solely to protect his family, especially his daughter Airi, who remains his absolute priority.

Originally a knight of the Freyjagard Empire, Bernard resigned upon foreseeing the Empire's retaliation against the Seven Light Faith. He initially rejected Tsukasa Mikogami's recruitment offer, fearing duties that might separate him from Airi, openly admitting his resignation was a "selfish" but non-negotiable choice to stay with her. Tsukasa persisted, guaranteeing Bernard could be stationed near his hometown to maintain proximity to Airi and framing their alliance around dismantling birth-based inequity. Bernard ultimately accepted leadership of the Faith's knights under Tsukasa's explicit condition that family remained his foremost obligation.

Bernard exhibits calm judgment and courage in crises. During Duke Gustav's attack on Dormundt's noble district, he defied expectations by rescuing nobles hostile to the revolution, asserting true equality demands protecting even opponents. This action demonstrated his commitment to moral consistency. His leadership earned deep trust among soldiers and recognition from Tsukasa for his reliability and tactical composure. Bernard later joined the protagonists' inner circle, accessing confidential strategies, marking a shift from personal isolation to engaged leadership while balancing familial devotion with the revolution's broader goals.