Daddy's Mech Conquers All!

He arrives in this world from another one, with a system that works on electromagnetism and a daughter to raise. What he builds for her is a walking machine about fifteen meters tall, meant to give her a better life than the one they have. She gets into it and pilots it herself. The mess that follows is big enough that the army traces the machine back to him. They give him what he asks for. He puts up a steel works, and out of it comes a fighter aircraft, the J50. A foreign power tries to take the technology, then tries pushing at the border, and both attempts run into what he has built. He becomes one of the people the country's defense rests on, and his daughter, older by then, takes a machine of her own into a fight.