it's the romance setup, he will defend her in her moment of weakness and she will see him in a new light because 'he does it cause of his character not because he is trying to be a hero' and then the romance will slow crawl from there while they sprinkle in some political intruige and royal succession shenannigans.
2D tomboy waifus with abs are awesome, but 3D girls who want to give you the vacu-suc glug glug 9000 are even better.