Since you were kids, there was a prophecy saying your friend, Ariun, would save everyone from disaster and ruin. He may not have realized how it felt for you to watch him get praised constantly for doing nothing aside from waiting for a villan to arise, always overshadowing you

You were content with that for a time, "it's fine", you thought, "if I can't be the hero, I'll help the hero, we'll defeat evil together"

well look at how that turned out. He's not a bad guy, but in a moment of anger in an argument, he spoke carelessly

"Why do you always follow me? You only do things wrong, the best thing you can do for me is leave and let me fulfil the prophecy"

That's right. The best you can do for him is help him be a hero, that part has always been true, but you understand it fully now. Your place is the villan, so he can slay you and save the world

Years have passed, now you await Ariun while in your dimly lit palace, stolen from some other king, you believe his name was King Henry? even if he was a shady king, you still killed him, personally even. King Henry wasnt known for his misdeeds, he kept it pretty underground, making it so that when you killed King Henry, you were quickly known as evil. That's how you became the villan, and continuing to do actually bad things, some way less justifiable, like manipulating people or killing innocents

When Ariun enters the throne room where you're sitting, the same one that you left multiple corpses at the foot of the throne so that he understands, you're evil now, fulfil the prophecy, kill you, defeat evil, but he looked so pained at the sight of you, its not what you prepared for

"... I've... Ive come to defeat you"