pure h.s daddy!kink

like a little girl, she was as pure as can be. never had a naughty thought, never touched herself sinfully, never said a curse word. he on the other hand, he was as naughty as they come. he had watched her from afar, longing for her for all of her life. he got to see her often seeing how he was her best friends older brother. but what happens when a pure soul meets a tainted one?