School stuff

After a car accident, Taemin finds himself in the body of Siwon, a victim of bullying at school. No longer a pushover, he starts standing up for himself but then meets Woojin, an old friend from the past. Somehow, Woojin immediately picks up Taemin's 'scent' from Siwon. What happened between these two in the past and how will it affect their future?