If you do something steadfastly, you do it with a lot of determination and without changing your mind.
Steadfastly makes people think of being very strong and not giving up.
Examples:
She worked steadfastly on her project.
He steadfastly refused to give up.
They walked steadfastly towards their goal.
The little boy held his teddy bear steadfastly.
She steadfastly believed in herself, even when others didn't.
The superhero steadfastly protected the city from harm.