The Great Disaster (大災害, Daisaigai) is an event that happened two hundred and fifty years before Year 198. The incident involved flames exploding around the world, devastating it and leaving most parts of the planet uninhabitable. Continents were torn apart and some nations were utterly obliterated. As a result, survivors fled to the Tokyo Empire, which remained mostly stable during the period.
The Holy Sol Temple and Haijima Industries created the Amaterasu generator, ensuring power could sustain the Empire. This power let the Empire develop further and allowed for more migration from the outside world. This lead to cultural changes within the Empire, such as it becoming customary to refer to others by the first names as opposed to their family names.