to make them all feel better about them self. ONLY READ IF YOU HEARD MY MESSAGE! (btw kinda sad =,( ) the reason shigaraki says, "there's a secret side to everyone's story" is because shigaraki killed his family by accident, toga wifey ate a bird and her parents hated her, kurogiri used to be human until he found out his quirk, and dabi.. we all know he's secretly touya todoroki and shigaraki wants to let everyone know, there's always a secret side to a story.
