Michio left Tatsumiya Island about five years before the series starts, heading out with his father Youji to fight for humanity rather than just defend their home. He became an ace pilot for the Human Army and took in Canon Memphis, a young orphan he rescued during the Dublin battle, training her himself.
His real reason for leaving was sacrifice—piloting his Fafner Mega Therion has been slowly destroying his chromosomes, and he willingly endured this degradation so his father could study his cells and develop treatments to extend the lives of other Fafner pilots. His codename in the military was "666" (Triple Six).
When Michio finally returns to Tatsumiya, he immediately shows his true colors by turning against the Human Army when they move to destroy the island. Turns out he never stopped loving Toomi Yumiko, his classmate from before he left, and the two finally get a chance at happiness together—or at least moments of it between all the fighting.
His father was stationed at the New United Nations' Moldova Base, while his mother stayed behind on the island. She died in the first Festum attack along with Kuramae Karin. After returning home, Michio eventually trades his Mega Therion for a Mark I to continue piloting.
Content compiled by AnimeList.moe from publicly available sources.
