Sayara Yamanobe serves as a scientist and research director at Aoyama Pharmaceutical Company, spearheading bacterial research while covertly conducting extensive illegal experiments in human cloning to achieve immortality. She exhibits a complete disregard for ethical principles, prioritizing rapid results and absolute secrecy at any cost. Her methodology involves performing surgeries and vivisections on fully conscious subjects without anesthesia, revealing sadistic tendencies where she derives palpable pleasure from prolonged torture over swift execution.

Kouki Maeno stands as her first successful human clone, created using memories from the original Kouki who perished during an experimental vivisection. This clone's escape during a facility transfer ignited her conflict with Rin Asougi. Numerous failed cloning attempts preceded Kouki; these flawed specimens remained confined within the facility until Rin's intrusion accidentally released them. The escaped clones attacked laboratory personnel, including Sayara. She nearly died in the assault but received a last-moment rescue from Apos.

Driven by her quest for immortality, Sayara developed biological weapons. In 2011, she returned to kidnap Rin and attempted a biological attack on Japan. Kouki Maeno thwarted this plan by consuming a Time Fruit, transforming into an angel and sacrificing himself to stop her. During this confrontation, Kouki critically wounded Sayara. To survive, she consumed a Time Fruit herself and transformed into an angel. Apos, however, immediately betrayed her, extracting her Time Fruit and causing her permanent death.

Sayara possesses brown hair and yellow eyes. She maintains a professional scientific demeanor yet displays eccentric behaviors like wearing her lab coat and carrying a clipboard outside the laboratory. Her communication is consistently blunt and direct, often unsettling others. She remains singularly focused on her research objectives, demonstrating unwavering passion for her work irrespective of its unethical nature.