"My cunning, crafty younger sister and my hardworking older sister—how did it come to this? It's all because my sister has a hobby of stealing other people's things! She even chased me all the way to the magic academy and tried to take my fiancé, so she ended up with such a fate!"

My younger sister, who is always unfair and takes my precious things, is the younger daughter of a duke's family, while I am the elder. I have always been troubled by her. Thinking that my foolish younger sister wouldn't be able to enter the magic academy, I enrolled in the academy to get away from her and moved into the dormitory. I thought, "Finally, my engagement to the Crown Prince has been decided, and once we marry, I'll be completely separated from her." But then, what? She got in through the back door? My younger sister, who loves stealing other people's things, continues to steal the boyfriends of her classmates, and I even end up being scolded as her older sister to do something about it... And then my younger sister starts hitting on the Crown Prince, and I'm truly furious. What is the final measure I take?