Kiriku arrives later in the story as a new transfer teacher at Kazalumu Beast Sanctuary. He poses as a poison expert, often unsettling others with an eerie smile. His true allegiance lies with the secretive Psi-Gamul, operating under Damiya's covert orders to infiltrate Kazalumu for undisclosed objectives.

His background involves significant trauma: his younger sister, Tahya (also spelled Tayan), died from poisoning involving a Wajyaku plant. This event profoundly shaped him. His childhood included foster parents who accepted him solely for financial gain; they later attempted to abandon him and his sister once payments ceased, fostering his mistrust and hardened demeanor.

Initially viewing Erin as a strategic asset due to her unique ability to communicate with Royal Beasts, Kiriku plans to exploit her potential as a weapon. However, his perspective shifts as he observes her empathy and determination. Her physical resemblance to his deceased sister and her compassionate nature—especially her unwavering kindness toward opponents—gradually weaken his resolve to follow Damiya's orders. This conflict culminates in his decision to protect Erin, defying his superiors and marking a pivotal turn in loyalty.

During the political conflict's climax, Kiriku sustains injuries trying to persuade Erin to flee for her safety. When she refuses, prioritizing her responsibilities to prevent bloodshed, he respects her choice. He encounters the adversary-turned-ally, Ialu, and they temporarily join forces to overcome Damiya's soldiers. Kiriku uses his mask to disguise Ialu, facilitating the latter's mission to confront Damiya directly. After the conflict resolves, Kiriku survives, abandons his previous affiliations, and transitions into a new life as a traveling doctor, symbolizing his departure from violence and pursuit of redemption through healing.