- Season 1
A bizarre murder occurs when an expensive pet turned into a monstrous creature and killed its owner before dying itself. At the crime scene Dan Dastun explains that animals, even simple cats and dogs, are nearly extinct in Paradigm City and thus wildly valuable. Meanwhile, Dorothy brings brings home an abandoned kitten named Pero after finding it in an alley during a rainy day and becomes attached to him. Roger begins to have his doubts when the kitten dirties his office, but also notices a positive change in Dorothy's demeanor ever since brining him home and wonders if the kitten has simply stirred up memories of the girl Dorothy was modeled after. When Pero's owners show up to reclaim him, Roger tries to negotiate with them to no avail. As Roger advises Dorothy to personally return Pero to the family, a man in an aircraft captures Dorothy with Pero and kills the distraught owners. As she dies, one of the owners pleads hopelessly with the man to return "Roy".
Through his informant and Angel, Roger learns that the man is named Eugene Grant, an alchemist that was entrusted with precious scientific memories by Paradigm Corporation to genetically revive rare animals. Eugene double crossed Paradigm and began experimenting on humans. Eugene shows Dorothy his experiments of human and animal genetic manipulation, revealing that Pero used to be a human child named Roy belonging to the family that he had just murdered. As Roger traverses Eugene's lab and learns from Angel about what Pero really is, he comes to believe that Dorothy sensed that he, like her, was an abandonded creation which is why they became so attached.
Roger summons Big O when an experiment, known as the Chimera, is unleashed by Eugene to kill them. The ensuing battle between Big O and the Chimera destroys the lab and everything inside, setting it ablaze. Dorothy, apprehended by Eugene, begs Roger not to attack the Chimera because Pero was the base of the experiment. The Chimera kills Eugene when Dorothy calls out to it. When Dorothy asks it to stay with her, the Chimera instead returns to the burning lab where it perishes. In the morning, Dorothy confides in Roger as she asks about her own identity and memories. Roger reassures her, telling her to treasure her memories, including those of Pero, and Dorothy thanks him.
- Megadeus: Big O, Chimera
- Aircraft appearances: