One night Chaos Organism encountered a swarm of fireflies and turned them into ravenous killers. The swarm quickly fed on one man's car leaving only the tires. Musashi and Keisuke arrived the next day to the site only to find the chaos mutated fireflies attacking them. They were about to be eaten alive in their car when Musashi shut off the engine, making it invisible to the swarm. Shortly after the two of them went out to track the swarm, Koji and Ayano were sent in one of the fighters to assist them. The swarm took notice of the fighter's heated engine and formed into the monster Chaos Bug after being fired at. As Chaos Bug tore through the the local town, EYES tried to defeat the creature to no avail. Having no other choice, Musashi turned into Ultraman Cosmos to do battle. Even though Cosmos was able to easily out manuver it, Chaos Bug caught the hero by surprise when its Chaos Absorber redirected the Luna Extract with great force. Cosmos quickly went from Luna to Corona Mode and started to beat Chaos Bug mercilessly. After assaulting Chaos Bug, Cosmos used the Naybuster Ray to blow the Kaiju to pieces.
- Suit actor: Toshio Miyake
- The back of Chaos Bug's head is shaped like a skull. This was purposely invoked as a sign that the monster was entirely evil.
- Chaos Bug's suit was modified to create Banpira.
- This episode was featured in episode 146 of New Ultraman Retsuden, "Type Change Hero! Tiga and the Warriors of Light".
- In an alternate scenario provided in a manga, the Chaos Bug was defeated by JADF's Robo Baltan. However, some of its exploded debris slipped into the robot, which allows Chaos Header to hijack it in the process.
- The Chaos Bug came from Hotarugahara (firefly village), Keisuke Fubuki's hometown. This village previously appeared in Ultraman Ace where another firefly monster Hotarunga was brought into existence due to the meddling from an extraterrestrial entity.
- Chaos Bug was proposed by Hideyuki Kawakami as an entirely malevolent opponent for Cosmos Corona Mode to fight, while its merger with inorganic substance is an inherited plot from episode 4.
- Powers and Weapons
- Technology Consumption: A swarm of these can attached themselves to any light and heat source from any technology (mainly vehicles) and consume them, leaving behind tires.
- Energy Absorption: These swarms can absorb energies or laser shots.
- Combine: These swarm can combine themselves into the gigantic Chaos Bug.
- Height: 53 m
- Weight: 57,000 t
- Origin: Hotarugahara
- Powers and Weapons
- Antennae Energy Beams: Chaos Bug can fire blue energy beams from its antennae that can cause small explosions.
- Entrapper Stream: Chaos Bug can emit a blue stream of energy from its left hand that can entrap small objects.
- Chaos Absorber: Chaos Bug can absorb beams like Ultraman Cosmos's Luna Extract and redirect it through his eyes using large amounts of chaos energy in its abdomen.
- Luna Extract: Using this abilities, Chaos Bug can fire Ultraman Cosmos's Luna Extract through his eyes. However, this is more of a damaging move than a calming move.