Mid lives with his parents in Cid's home. When the meteorites land, he is locked inside Cid's house with his mother and father. After the Creator has been felled, Cid takes Mid to the underworld to visit Luca (whom he appears to have a crush on). He helps her find a missing part to repair the Falcon.
Spoilers end here.
Mid at the Dwarven Castle's Crystal Chamber with Cid and Luca (Wii).