Before I Knew It, I Had Stolen the Dark Lord's Heart

Seeing the relationship between Duke Willow, the Sword of the North, and her father who's his guardian knight, Celine has been looking forward to meeting her lord, Damian. However, the Damian she encountered was a skinny, frail boy with a bright smile that belied his Northern Majesty. To fulfil her duty as a guardian knight, she decided to take her lord's side, no matter what kind of person he was. But there's something fishy about this frail boy... --- Ten-year-old Celine Mars dreams of becoming a great knight escort just like her father. She’s set to serve under Damien Willow, the heir of a powerful Duke. There’s only one problem—he’s a total weakling, or so she thinks. Celine vows to train the poor, defenseless Damien to stand up for himself, completely unaware of his real strength. Meanwhile, Damien instantly takes a liking to Celine, finding her cluelessness and pure intentions both amusing and endearing. When will Celine finally realize she’s got the wrong idea about Damien?