Well, it could be about a BTS member accidentally running into a gymnast YN at a sports event. Maybe they get to know each other gradually and BTS is inspired by YN's dedication in gymnastics. It could also involve YN getting a chance to perform at one of BTS's concerts, creating a unique and exciting plot.
One way is through a charity event. BTS is often involved in charity work, and YN could be performing at a gymnastics - related charity event. They meet there and start interacting. Another way could be if YN is a back - up dancer for another K - pop group and during a big K - pop concert, BTS and YN cross paths.