You can’t go wrong with joining a sports team, and once you become a member of the Track Team in Persona 3 Reload, you meet Kazushi Miyamoto, one of the team’s star athletes. He represents the Chariot Social Link in P3R.
Persona 3 Reload Chariot Social Link Guide (P3R)
Chariot can be started on 4/23 at its earliest by visiting the Track Team. Enter the Corridor door at School Building 1F, head straight up to the Gym Hallway, and enter the Practice Field. You’re offered to join the Track Team, so accept it to start the Chariot Social Link.