He is just an ambitious coward who evades the throne and lets his sister act as a shield.
He just wanted to stay in the research institute and spend his whole life working on blueprints, but he was thrown to the front line to observe the brutal and inhumane war. After he came back, he could no longer make any weapons for the country.
He was thrown into an enemy country by a dead woman to steal things, but he stole someone back.
He was locked up in a research institute, and someone happened to steal his research results, so he decided to be stolen and travel around the world.