I had a blast making this. It was 95% done during classes with only my writing pencil and black ballpoint pen, tugging the paper under a textbook and making a few traces at a time.
I'm happy to say that I didn't use any reference for this and this is the result of her just being on my mind all the time. Who knew that she would help me get better at drawing, she really is the greatest.
That said, the image itself is compressed because of the 4 MB file size limit, so if anyone wants to see the full version:
https://mega.nz/fm/KN5SmYiIHappy Valentine's Day Yui, I love you so much!