Exaggerated: In order to mantain his independence, Rune must slaughter Llyrr, Evulz, every single knight, soldier, assassin and Mook they command, and reduce each of their strongholds to a smoldering wreck. Many of their strongholds are in cities and fortified towns, vital to their respective countries and communities.
Downplayed: Both sides are almost identical, with little characterization and no reason not to kill both. That, or the game lets you to keep playing after destroy a side, making the destruction of the other side the only way to continue.
Lampshaded: "Well, I guess you could pick no side but who'd be crazy enough to do that?"
Invoked: An unforeseen third party is hoping that Rune would take this option and is willing to frame the two sides against Rune.
Defied: The two kingdoms realise that Rune IS capable of wiping them out and decide to either leave him alone or make peace with each other.
Discussed: "You'll have to pick a side, Rune. You can't possibly take them all!"
Conversed: "Wh-What do you mean, he's killing everyone?!"
In taking out the Kingdom of Lrright and the Empire of Darkonn, Rune leaves their respective realms in tatters, as survivors try to scrape together their own little parcels of land and fill the power gap. Instead of ending the war decisively, he's prolonged it indefinitely.
Both sides have been made morally gray, so Rune ends up being the worst person of them all.
Reconstructed: As Crapsack as the world becomes, Rune believes that this state of affairs is still better than what either Llyrr or Evulz would have brought if they had achieved their goals.
Played For Laughs: Fairy Companion Blythe keeps bringing up the "Plan C: KILL EVERYONE" option whenever Rune is faced with a decision to make. Any decision.
Played For Drama: Rune is made fully, painfully aware of the potential ramifications of killing off the two most powerful, influential leaders of his time. His family lives in one of Lrright's provinces, along with most of his childhood friends, and most of them are staunch believers in Llyrr's goal of ultimate peace. On the other hand, he sees firsthand that not everyone living in The Empire is evil, even among Evulz' soldiers... And some of his other friends are among their ranks. Stopping both Llyrr and Evulz will mean putting everyone at risk — but is the risk of letting one of them succeed far worse...?