Micro-Oxygen (ミクロオキシゲン?) is a powerful fictional chemical compound which is presumably created from the atmospheric elemental gas oxygen. It is a major ingredient of the deadly Mikuro OkishigenOxygen Destroyer.
Daisuke Serizawa unintentionally developed a device called the Oxygen Destroyer while studying and experimenting with oxygen. Serizawa presumably discovered and experimented with micro-oxygen during this process, however the substance is never mentioned by name or alluded to in the film.
42 years after the events of 1954, physicist Kensaku Ijuin rediscovered the chemical compound used in the Oxygen Destroyer through his own experiments, dubbing it Micro-Oxygen and intending to use it to benefit humanity. Ijuin said that micro-oxygen could allow deep-sea divers to use lighter tanks that contain more oxygen, and an experiment showed that any fish raised in water containing micro-oxygen would grow much larger than normal fish, potentially alleviating the world's hunger problem. Ijuin admitted that micro-oxygen atoms were capable of penetrating any material and unleashing large amounts of energy, and would make a very effective weapon despite not being intended for the purpose. Yukari Yamane, heeding a warning from her aunt Emiko, asked Ijuin if he was aware that micro-oxygen was very similar to Daisuke Seizawa's Oxygen Destroyer. Ijuin stated that he consulted some of Serizawa's surviving work during his experiments, but never intended to recreate the Oxygen Destroyer, because his studies performed on the underwater soil where the Oxygen Destroyer was fired revealed that it could have reduced Tokyo to a graveyard if used on land. Kenichi Yamane approached Ijuin and asked him to use micro-oxygen to re-invent the Oxygen Destroyer, believing it was the only way to destroy Godzilla before he could destroy the world. However, Ijuin had already discovered that the Oxygen Destroyer mutated several prehistoric crustaceans in Tokyo Bay in 1954, and that these creatures had evolved abnormally to manipulate micro-oxygen within their own bodies. Hoping to stop the creatures, Ijuin ran more experiments with micro-oxygen and discovered that it liquefied at low temperatures and was rendered ineffective. Ijuin urged the military to use freezer weapons against the creatures, as it should neutralize the micro-oxygen in their bodies and kill them. However, the creatures combined together into a single giant monster, and the chemical composition of their bodies changed once more. Ijuin noted that the creatures had become the living Oxygen Destroyer, dubbing it "Destoroyah."
- Though the exact chemical composition or processes of micro-oxygen are never discussed, it is implied that micro-oxygen atoms are simply miniaturized oxygen atoms that contain more chemical energy than normal oxygen atoms. When weaponized as the Oxygen Destroyer, micro oxygen can cause violent and corrosive chemical reactions that penetrate or disintegrate virtually any material.