[Seneschal]

Another example would be the main plot of Obsidian's Pillars of Eternity, SPOILERS AHEAD, where children throughout a region start being born soulless. The "hollowborn" have no drive if their own and behave almost as if in a vegetative state. Since the setting's entire mythology and magic system is based on soul-manipulation, a group of animancers (soul-scientists) come up with the idea of binding animal souls into hollowborn. Initially it works, allowing the hollowborn to move, feed themselves and such, but only at the most basic, instinctual level. Eventually, they all go feral and roam the countyside in murderous packs as "wichts."

The inhabitants of the afflicted land call this event Waidwen's Legacy and consider it to be punishment for then blowing up the avatar of a god in a recent war. The main plot involves discovering that the Legacy is manufactured by an ancient cabal who use animantic relics of a long-dead civilisation scattered throughout the land to redirect souls returning from the Wheel, and use them as fuel to empower their own goddess - a conspiracy that the avatar tried to stop before being blown up! In turn we also discover that gods themselves are (relatively new) animantic constructs made from mass ritual sacrifice by the aforementioned ancient civilization.

So, in conclusion, you can do lots of stuff if you treat souls as blobs of energy parasitizing human bodies. Children born soulless isn't much of a plot seed by itself, but its implications are many.