First Level: Introducing the BBEG early on

The PC, all freshly and rolled, is hugged by their mother who tells them to stay away from women loitering in alley ways, and their little sister cries, begging them not to go.
But a few feet beyond the hamlet gate they encounter the BBEG and having this one window of opportunity to exterminate the greatest threat they will ever encounter, get a charisma check to resist having their will dominated.

Success and the BBEG immediatly flies on into the village to enslave someone else...unbeknownst to the PC.

Failure is likely if they, like most PCs have a player who decided that Charisma could be the lowest dice roll.

Of course the other players characters are not from this village they only get to listen to the DM describe what is happening, so when the arrive in the PCs home village of Mucketybucket they find that a lone, blood-soaked, half naked berserker is beheading the last of the villagers (the little sister) so they either kill the BBEG controlled Adventurer, or save them from themselves, maybe saving the little sister either way. If the only survivor is the little sister, the player starts off, not as the wannabe hero, but as the little sister, dependant on the party for survival, and horribly traumatized by the nightmare that will haunt her to the end.

The BBEG flies off immediatly realizing the threat posed. And now if the Adventurer has survived enslavement, they get the added trauma of having butchered their loved ones.