Toshiaki Hayami served as a scientist within the Cronos Corporation at the Relic's Point facility, assigned specifically to the deepest levels researching the bio-technology of the Creators—alien beings who engineered life on Earth. He and his colleagues, led by Dr. Yoshio Odagiri, were forcibly indoctrinated into Cronos and held no loyalty to the organization, secretly conspiring to sabotage it from within. As part of their indoctrination, Cronos infected Hayami and the others with a lethal virus that boosted their mental capabilities but required regular antidote doses from Cronos to prevent death. The sole alternative for survival was undergoing Zoanoid processing, which would subject them to the psychic control of the Zoalords.

Hayami actively aided Sho Fukamachi, Agito Makishima, and their allies, manipulating Relic's Point security footage to conceal Agito's infiltration alongside Sho and Mizuki Segawa. After Relic's Point's destruction and Dr. Odagiri's death, Hayami and the surviving scientists were forced into hiding. Following Cronos's global takeover, they focused on finding a cure for the virus before their antidote supply ran out. When time expired, they risked the dangerous Zoanoid optimization process to survive. This altered process created Lost Numbers—Zoanoids surpassing standard variants in ability and immune to Zoalord psychic control. The optimization carried extreme risks, leaving Hayami as the sole survivor among the scientists.

Post-optimization, Hayami became known as Bio-Freezer, wielding cryogenic abilities. He could release bursts of supercooled helium over a radius, freezing enemies solid. This power proved especially effective against Enzyme III-type Zoanoids. Generating the helium burst required significant preparation time, however, leaving him vulnerable during activation. His combat capabilities generally fell below those of Guyvers or Hyper-Zoanoids, necessitating careful tactical planning during engagements.

Bio-Freezer later reunited with the Guyvers and their allies, including the rogue Lost Number Aptom. His presence alarmed the Zoalords, prompting Zoalord Cabraal Khan to devise a plan to regain control over Aptom. Cabraal engineered a Zoanoid implanted with his own DNA and deployed it against the Guyvers. Aptom absorbed this Zoanoid, inadvertently integrating Cabraal's DNA and falling under his psychic control. While controlled by Cabraal, Aptom attacked and killed Hayami. In his final moments, Hayami used his freezing power to immobilize Aptom, creating an opening for Sho Fukamachi (Guyver I) to break Cabraal's control. This sacrifice ensured Aptom's return to the allies' side.