Gilthunder's Sister (Seven Deadly Sins fanfic)

Seven Deadly Sin's is a manga that was turned into a Netflix-original anime. I highly suggest checking it out if you have Netflix. It's a very enjoyable anime. Anyways...
Hitomi was Gilthunder's younger sister. Being the second child and daughter of the great holy knight leader, she was not paid much attention to. Her father focused more on Gilthunder than he did on her, which made her lonely and sad most of the time. She never had any jobs and was never trained to do anything. Really, the only thing she had was her brother. He loved Hitomi so much, he taught her everything and let her tag along on his job of watching Princess Elizabeth. But little did Gilthunder know that his little sister would take his knowledge and use his training to go above and beyond what he could do.