Jonson began as an ordinary insect dwelling in the sewers beneath Hole. Exposure to residual magical smoke pollution within the wastewater triggered a mutation, transforming him into a monstrous entity. Starting roughly dog-sized, he rapidly expanded into a giant humanoid cockroach. His form features greyish-brown skin, a large black head with a beak-like mouth housing human teeth, sensory spikes on his limbs, and a pair of torn sneakers. This mutation endowed him with significant physical durability, formidable strength, and considerable speed. His extremely resilient exoskeleton can shatter knives on impact. He also developed heightened intelligence akin to a young child and gained the ability to communicate with and command ordinary insects. Initially, Jonson served a human resident of Hole, employed to dispose of corpses from victims killed for their believed "Black Pearls." During this service, he displayed aggressive behavior, attacking and consuming anyone encountered in the sewers. This brought him into conflict with Kaiman and Nikaido during a rescue mission. Jonson overpowered Kaiman until his owner was killed, revealing the "Black Pearls" were merely waste products. Following this encounter, Professor Kasukabe took Jonson in for study of his unique anatomy. Using specialized radio frequencies detectable only to insects, Kasukabe trained Jonson to become docile and obedient. Jonson developed genuine loyalty and affection for Kasukabe, behaving like a devoted companion animal. His training enabled him to vocalize the single word "Shocking!"—a phrase inspired by creator Q Hayashida's reaction during a baseball game. Jonson became Kasukabe's constant companion, assisting in laboratory work and joining a baseball team alongside Kaiman and Nikaido. He accompanied Kasukabe to En's mansion, where both were imprisoned. During captivity, Jonson directed a cockroach to unlock their cell using his insect communication ability. After escaping with stolen uniforms, they traveled to the Hydra Forest to visit Kasukabe's wife, Haru. Later, Jonson witnessed Aikawa transform into Ai Coleman. When Coleman attacked Kasukabe, Jonson intervened and sustained severe injuries, including disembowelment. Haru intervened, saving both Jonson and Kasukabe by transporting them to Hole, where Jonson subsequently recovered.