I haven’t done it yet, but ideas I’ve thought about are:

• on a flying ship (party, traveling, etc) and it’s attacked and crashes
• they are part of a town and witnessing an execution, coronation, etc, and someone attacks or stops the event scattering those watching and forcing people to fight for their lives
• dead and in a hell when they are given the opportunity to return to life and avenge their deaths
• plucked from their lives and brought to limbo where they are informed that their destiny must be fulfilled as they are now awakened souls who were sent to the realm to fulfill their duty as agents of good to stop a rising darkness and then they are sent back to reality with a drive to meet up at a certain place to gather their group and begin their duty