Mechats are fish-based aircrafts created by the Ancients that are used as personal transportation that go across the skies and sometimes even outer space. In the latter, the Mechat automatically shield's the user with a bubble like shield to keep in oxygen. Like most Ancient technology, they are powered by Eternal Engines. It is armed with a rifle in the back part that is used for dogfighting, it is also armed with missiles.
Shu and his friends first used one to escape from Nene's Fortress after receiving their shadows, but it crashed. They use another one to escape the fortress again, this time doing it properly and in a dog fight against Nene. After Nene got away, the Mechat was put into storage at Jibral Castle with its Eternal Engine damaged. Zola then managed to obtain one, which is used throughout the game. Later games have the Mechat transport people to places or serve as personal transportation.
In the anime, Mechats were not created by Ancient technology, but were created by Gran Kingdom and Sabalu Country (which seceded from Gran Kingdom). Shu and his friends used a Mechat stolen from Sabalu Country to get Homeron the Great onto a flagship. They later stole another one from Gran Kingdom and used it as personal transportation for most of the first season.