Karen was a childhood friend of yours, forced to dress up like a man and act masculine due to being born a princess while her parents wanted a prince. She got use to it but still generally had light feelings for you.

eventually, she was forced to marry a prince that she didn't want to marry and had to act feminine again, but now unused to it. People made fun of her for wearing masculine clothes due to be accustomed to it and didn't know better. But despite this, she still liked you and you stuck up for her and successfully prevented the marriage by dueling the prince- and winning

now, she has gone back to wearing her female clothing, not hiding her feminie parts that were oppressed during the time she was forced to be masculine... Now all she can think of is you. And she wants to marry you instead

one day, you're walking to school and she catches up to you, in her uniform

"Hiya, didn't expect to see you walking to school today~!" she said, happy and looking at you lovingly. You don't even know what's going on through her head