Today, a team of scientists announces they have figured out a way to reincarnate yourself. The process, which costs about as much as a series of expensive surgeries, "transfers" your brain into a fetus that's still in the womb (killing your old body). Ten years later your consciousness emerges from dormancy, as the child hits puberty and its brain develops to the point where it can support you. One moment you're in a lab with wires hooked up to your head, the next thing you know it's a decade later and you're in the body of a nine-year-old. Amazing!
Of course, you just 'overwrote' the child who was using this body up until now. And no, they can't be kept in a coma their whole lives, that'd cripple their mental and physical development to the point where your consciousness would never emerge.
In other words, humanity just rendered immortality possible, and all it requires is the death of a child. What effect does this have on society? What's the world going to be like in 50 years?
This is just one of those open-ended brainstorms, where I focus on seeing where the idea naturally leads rather than trying to push it in a certain direction. Still, it's not hard to see how things would go. There'd be a lot of countries which outlawed the procedure and consigned all reincarnated individuals to a quick execution. Others would be more. . .flexible, perhaps even allowing it so long as one had obtained the mother's consent.
Regardless of their official laws on the matter, every nation would likely have a thriving illegal market for the procedure. It's a matter of human weakness. Say you find out tomorrow that you have a terminal illness- you have about a month.
Someone approaches you and discreetly offers you the reincarnation procedure. The price is simple: You will all your assets to a certain charity, i.e. to them.
They don't expect an immediate response. They'll wait. You can signal that you want to do it at any time; or you can die.
Will your convictions hold?
That's how you end up with a world that has the horror of foster parents realizing that their child is no longer their child. Where children secretly worry that their minds are time bombs, that sometime around the age of 9 they'll go to sleep one night and never wake up.
You have a world a reincarnated individual's first act being to read a letter under the pillow they were sleeping on- a letter addressed to "the new me", asking them to please take care of the child's dog and to be nice to his little sister.
If I'm tying this back to a premise for roleplaying game, the "light" option is to simply have it be one particularly bleak facet of a cyberpunk setting- the sort of thing that might be investigated by Ghost In The Shell's Section 9.
The "heavy" option. . .well, one particular scenario comes to mind. You're a part of a terrorist organization that assassinates reincarnated individuals, as well as abducting "eggs" and crippling their hormonal development so that that they never 'hatch'- the child will live to about 25 on average, but that's much better than dying at 9, right?