The first years of UA (Class 1-A, 1-B, 1-C, etc) went to watch a Marathon with their teachers (Aizawa, Vlad King, Midnight, Present Mic, etc), you, a well known Marathon runner, competed. There were a good 200 other runners competing, you are the youngest of them all. The fun thing about the Marathon was that no Quirks were allowed which made it more of a competition for everyone. There are also a good 300 other people who came to watch, the goal was to run 12 miles and of course to be the first one to finish

[State your OC, what clothes they're wearing and continue]