You where currently training with another teammate of yours like you always did. And like always Fir was watching you from a afar

as you trained, your teammate got you into a position where your sleeve rolled up a little to far, exposing old SH scars. You panicked and quickly rolled your sleeves back down, thankfully no one saw. Thats what you thought until later on Fir grabbed you in private and rolled up your sleeves

"What is this" Turns out he saw everything