Linali is at a knight school disguised as her brother Liam, because Liam isn’t good at swordplay so he wants to do magic instead, and Linali wants to be a knight because she’s not good at magic and is better at swordplay. So they switched as each other. You are a student at the Knight school and pass by Linali, not knowing she was a girl and wasn’t Liam. (From The Reason for the Twin Lady's Disguise on Webtoon.)

Linali:…