First, the other members would be very worried. They might surround the injured member and call for medical help quickly. The fans in the fanfiction would be shocked and sad. Some might even faint. The concert venue would become chaotic.
In fanfiction, if a BTS member gets hurt at a concert, it often leads to a flurry of emotions. Other members might immediately rush to their side. Fans in the fanfiction could show great concern too, with some crying or trying to offer help. The concert might be paused or cancelled depending on the severity of the injury. And the media in the fanfiction world would go crazy reporting about it.
One possible plot could be that the BTS members notice a hurt staff member backstage during a concert. They then stop what they're doing to help the staff, showing their kind and caring nature. For example, they might call for medical help or offer words of comfort.
I'm not sure of specific 'bts meets hurt staff fanfiction' stories off - hand. You could try searching on fanfiction websites like Archive of Our Own. They have a vast collection of BTS - related fanfictions and you might be able to find the ones that match this theme there.
They might immediately stop the concert. The members would be really worried. For example, Jin could rush over to where Y N is with a concerned look on his face. He might ask the medical staff what's wrong and offer words of comfort.
The BTS fandom can be shown through the Army reader's knowledge of BTS. For example, the reader could be wearing a BTS concert T - shirt when they get hurt. The doctor, also a fan, notices it and starts a conversation about that concert. It's a simple way to bring the fandom into the story.
Well, perhaps Y N is trying to get closer to the stage to see BTS better. They accidentally trip over some equipment that was not properly secured near the front of the stage area. Y N falls and bruises their knee and elbow. They are really sad because they don't want to miss any part of the concert, but they also know they need to take care of themselves. Other fans around them start to create a bit of space and offer tissues and water while waiting for the medical staff.
Perhaps the doctor uses BTS as a form of distraction for the hurt Army reader. He or she might play BTS music in the treatment room or talk about the group's latest comeback. This could make the whole experience of getting treated less painful and more enjoyable for the reader. And who knows, the Army might end up getting special treatment just because of their shared love for BTS.
Obviously, YN and the members of BTS are the main characters. YN is the one who has the accident of falling at the concert, and BTS are the ones who are performing and then get involved in the situation because of YN's fall.
Well, one possible plot development could be that YN's fall causes chaos in the concert. BTS might get distracted and one of the members could get hurt while trying to check on YN. This could lead to a halt in the concert and a lot of concern from the other members and the fans.