VERY IMPORTANT, this is based off a true story, I'm in XC myself, and last year, my coach was telling my team about this girl Kayla Montgomery who was at the bottom of her team speed wise (her 5K was a 26 minute average, mine is about 22 minutes) and one day, she got diagnosed with MS and she went to her coach and said, "I don't know how much time left I have to run, but I want to run fast now." 

And a year later, she's one of the fastest high school runners in the US. 

Sounds like a gay Korean fanfic just waiting to be written, am I right?