Ryo Ishigami, known as Ryo, is a Japanese hunter pursuing a creature stalking the South American countryside. His troubled youth stemmed from neglectful parents: a crime reporter father and Professor Ishigami, his geneticist mother, both often absent due to work. This neglect fostered delinquency, leading Ryo into a motorcycle gang with little regard for his future.

On his fifteenth birthday, a mysterious woman attacked his gang. This figure was Bagi, a genetically engineered being combining human and mountain lion DNA. Unbeknownst to Ryo, she was the same creature he had rescued and raised as a kitten years before. Living with his family, Bagi displayed uncanny intelligence, learning to walk upright, write her name, and speak, ultimately leaving when her presence grew too conspicuous.

Five years after their reunion, Ryo became a hunter, partnering with Chico, a local boy seeking vengeance against Bagi for his father's supposed death. Ryo's own mission held deeper roots. He and Bagi had previously collaborated to trace her origins to the SuperLife Center lab. There, they discovered Professor Ishigami had created Bagi using recombinant DNA.

Tracking his mother to South America, Ryo and Bagi confronted her at the Cucaracha Research Lab. They learned she had been coerced into developing a genetically engineered, poisonous rice strain for biological warfare. Professor Ishigami sacrificed her life to ensure Bagi destroyed the samples. Witnessing her death but misunderstanding, Ryo blamed Bagi and swore revenge.

Driven by this misconception, Ryo hunted Bagi as she lost her human traits and grew feral. Upon capturing her, he stabbed her, only to find a locket around her neck containing his mother's final words in a note. This revelation forced Ryo to acknowledge his mistake. The next morning, Bagi's body was gone, footprints leading towards distant mountains. Accepting the truth, Ryo abandoned his vengeance, praying Bagi could live in peaceful solitude far from humanity.