I'm designing a campaign for a group of friends. One of the main plot hooks is a bunch of mercenaries that want to bring them to an oracle which gives them the first indication of the Big Bad. When they first encounter these mercenaries, I would prefer the players to trust them implicitly rather than have them go through three sessions determining if the mercenaries are lying this time.
I plan on having them start out in prison with secondary characters of their own. Their actual (campaign)characters would also be in this prison and be led away just before something happens to the prison. The players (as the secondary characters) would see this and when everything goes sideways, they meet the mercenaries who arrive too late to save the primary characters.
The players would have to try to get out of the prison, but it would be impossible for them to survive this -- thus these secondary characters perish -- after which they continue play as the primary characters.
This scenario gives them the chance to get to know the mercenaries under distress, which hopefully allows implicit trust when they meet them again later on. I know this is pretty railroady, but I prefer to DM that way in my first session of a new campaign, in order to make the setting clear.
Getting my players to make two characters is easy, but I would hate for them to spend the better half of a week making meaningful decisions about their character's backstories (they tend to do that) and then have them killed off in the first half of the first session. But, telling them that they don't have to bother, however, will spoil the whole story immediately since I tend to be pretty adamant about good backstories. That would cause them to not give a damn about the first character and the worst prison escape attempts are the ones where the person just rolls over.
How do I get them to invest enough time that they'll try hard enough to survive that they get to know the mercenaries, but little enough that they're OK with the character surviving less than a session?
The system is Starfinder and the setting is very loosely built on the one found in the Core Handbook.