DnD setting idea: All full, class-features-having Paladins (as opposed to paladins-as-knightly-orders, of which there are plenty but they're mostly made up of unpowered fighter types) are bound by their oaths to a specific Damned Innocent. Damned Innocents are those who, through no fault of their own, have become tainted by supernatural, free-will overriding, soul-devouring, capital-E Evil. People who are, in the most literal sense possible, destined to go bad, but they aren't necessarily there yet. We're talking young cambions (and probably even tieflings), children bred to be the hosts of Elder Things, demigods of evil deities, inheritors of generational warlock pacts, and the like. Bleak, hopeless, unfair existences. Lost causes, beyond the help of natural redemption. In any other world, the only mercy left to show them would be a painless death.
But here there are paladins.
There are signs that the Church and knightly orders know to watch for in new acolytes and squires, subtle connections to the divine less stable than that of a cleric. Of these identified candidates, only few are offered the special training necessary to become full paladin initiates, and even fewer complete their training. You do not become a paladin by accident. You must choose it, day after day.
As soon as a Damned Innocent is identified, they're paired off with a waiting paladin initiate who has completed their training. A bond begins to form between the two, eventually becoming complete and unbreakable, even by death, when the paladin formally swears their oaths. From that moment onward the paladin is responsible for being guardian, role model, and parole officer to their ward.
The bond is a symbiotic one. The paladin's holy magic cannibalizes some of the Evil infecting their ward, breaking it down and burning it for fuel. In exchange, the Evil's grip on the ward is suspended, allowing their true personality and will to assert itself.
Not every story of this sort ends happily. A paladin's bond gives their ward the chance to choose good, but it cannot make them do so. Sometimes a ward chooses, of their own free will, to embrace the full breadth of their nature. In these cases, the paladin's oaths to protect innocents force them to cross blades with the person closest to their heart in all the world.
Perhaps even more tragic are the Oathbreakers, once-paladins who abandon their oaths and draw on their ward's Evil directly for greater power with less responsibility, damning them both in the process.
It's not a perfect system. Far from it. It is as fallible as the men and women who make it work. But it is hope where there would otherwise be none.
And it's also a pretty incredible roleplaying seed between your party's paladin and sorcerer or warlock.
