So Cor's been taking csre of some kid, but no one's seen him until one day Regis asks him to bring the kid to the Citadel. The three bros find out no one has seen this kid because he's been abused and totured all his life by Niflheim before Cor smuggled him out.

Gladio, Noctis and Ignis decide to make attempts to help this poor kid recover, helping with physical therapy (Prompto can walk, but he looks like a clunky MT when he does so he's been in a wheelchair to dispel suspicion) and becoming more social because holy shit this kid is so quiet how did he make it this long