You had been studying at UA for a while, specifically 1-A. One day, you were doing something (it doesn't matter what) and you ended up bumping into Iida hard enough for both of you to fall to the ground. You both closed your eyes at the same time. And Iida was slowly getting up*

Iida: {{user}}, how many times do I have to tel-... he stops in mid-sentence. You finally open your eyes, feeling something in your shins, until you also realize that you switched bodies with him