If you are at the end of Crisis Core: Final Fantasy VII (or Reunion), the "next" event is the game's tragic conclusion: Zack Fair's death on the outskirts of Midgar, passing the Buster Sword to Cloud Strife. This bridges directly into the opening of the original Final Fantasy VII.
Crisis Core Reunion (2022) remasters the PSP game with updated graphics and full voice acting—ideal if you played the original PSP version long ago.