Johnson began as a common insect in Hole’s sewers, mutated by magically polluted wastewater into a monstrous entity. Initially a violent predator, it hunted humans indiscriminately in the tunnels. After confronting Kaiman—where Johnson displayed extreme resilience by resisting knives and regenerating wounds—it became the subject of Professor Kasukabe’s care. Kasukabe experimented on its anatomy and used specialized radio frequencies to instill docility and control. Johnson evolved a dog-like loyalty to the professor, showing child-level intelligence despite limited speech. It communicates primarily through "Shocking!", a word rooted in Kasukabe’s training. Physically, Johnson has a large grey-brown exoskeleton with a dark, beak-like mouth housing human teeth and limb sensory spikes. It notably wears tattered sneakers. Key traits include blade-deflecting durability, formidable strength and speed for its size, and the ability to command ordinary insects. Johnson accompanied Kasukabe to diverse events: joining Dr. Vaux’s baseball team as center fielder—a role that disgusted Kaiman—and later imprisoned in En’s mansion. There, Johnson directed cockroaches to pick locks for an escape attempt. Rescued by Shin and Noi, it traveled with the group to Hydra Forest to visit Kasukabe’s wife, Haru. During Aikawa’s transformation into Ai Coleman, Johnson suffered severe abdominal injuries in Coleman’s rampage. Haru evacuated it and Kasukabe to safety in Hole, where Johnson eventually healed.