Regis is a ruler, a powerful spellcaster, or both of the above. Wallis is a wrongdoer, who was once Regis’ lover, relative, or best friend. When Wallis does something utterly evil, Regis can’t bear to execute someone they still care about - so Wallis is exiled instead.
And, because fiction is never about plans going right, the exiled Wallis prepares for revenge and comes back worse than ever.
Examples of this trope include My Little Pony: Friendship is Magic; Baldur’s Gate; and the truly execrable novel ‘The Fifth Sorceress’ by Robert Newcomb.
So, the question is: what’s the ruler’s ethics here? The exile’s attempt at revenge inevitably puts many more people’s lives at risk. Maybe the ruler’s the worst villain here, for endangering people twice over.
First, mercy above justice. In the course of justice, none of us should see salvation; we pray for mercy, and that same prayer doth teach us all to render the deeds of mercy. If the ruler shows mercy to a wrongdoer, that’s a good sign.
But second, let’s demand fairness. If some people get away with light punishments for serious crimes because of whom they’re related to, or whom they befriended, or whom they used to date - that’s nepotism. We don’t enjoy that.
I’d like part of the answer of this to be that the ruler shows mercy when they can, as a habit, not just to the few people they’re close to. And the ruler’s mercy becomes them better than any crown, sceptre, or sword. The ruler’s mercy is one of the things that separate them from the wrongdoer, one of the qualities that their country values most in them. Their mercy is not a weakness.
Another part of the answer should be, I think, is that the exile punishment sometimes works, or could have worked. Maybe some wrongdoers make new lives for themselves in another country and accomplish something terribly important to someone, by walking along the right road at the right time or by using their skills to help instead of harm or by retiring to grow vegetable marrows and solve murder cases. Maybe the story of that one exile who came back with deadly vengeance isn’t the only ending. Maybe the ruler choosing the exile punishment was a risk, a risk on the side of mercy, and it failed in that one case - but it was a better kind of failure than some ruthless successes.
Above all, I don’t want the answer to the story to be, 'You know what would’ve solved this exile problem? Capital punishment. Lots of capital punishment. Summarily execute the wrongdoer instead of bothering with exile, and that would totally save the day.’ That’s not a solution that works in real life, and I find it fundamentally unsatisfying in fiction.
The ruler isn’t going to be perfect (work toward democracy already!). The wrongdoer could have a complicated personality, an admixture of light and dark as they make the choice whether to use their exile to strive for change or repeat their cruelty. The ruler faces a difficult choice, balancing mercy and justice, duty and passion, sentencing a loved one for a terrible crime, mediating punishment and payment and protection of the land, and hoping to the last hope that people can choose to change.
Mostly, I’d like stories of this type to let mercy be a good quality.
Full credit to Shakespeare and Portia.