Mikawa was initially a province with a sizable population. However, Lord Matsudaira initiated the Migration Plan to remove every single person in Mikawa except for him and a few key people and to replace them with automatons under his control.
During the night of April 19, 1648, Lord Motonobu begins the countdown to the destruction of Mikawa, wherein he uses the ether vein reactors in the Shin-Nagoya Castle to create a force that can wipe out anything within a large radius. Pope-President Innocentius, who arrived at Mikawa earlier that day, tries to stop this from happening by ordering his escort units from Tres España to intercept the countdown, but they were severely slowed down by Lord Matsudaira's loyal subjects Tadakatsu Honda and Kazuno and his automaton army.
After the Mikawa Meltdown, Mikawa is left with the Shin-Nagoya Castle completely decimated and without a leader. Under the orders of the Testament Union, Mikawa soon undergoes intensive repair, while the closest relative of the deceased Lord of Mikawa, Horizon Ariadust, is currently enrolled in Musashi Ariadust Academy as the automaton P-01s.
- Shin-Nagoya Castle (New Nagoya Castle) - A gigantic facility for the production of ether which provides power for people's abilities. Stands at 500m in height, and occupies a square-shaped area of 100 square kilometers. 
- Kyou-Nagoya Castle (Old Nagoya Castle) - A replica of the historical Nagoya Castle, located at the center of Shin-Nagoya Castle.
- ↑ Kyoukai Senjou no Horizon Encyclopedia, page 466.