Okay, since a lot of people think I can't write worth a damn and have nothing but negatives to say with very little helpful things, screw making a story, I'm making a challenge. A Kingdom Under Fire crossover.
Here are the rules.
1. It must have Regnier as the protagonist and at the height of his power. Doesn't matter how you put him in, just as long as he's brought to the world of your choice. Whether he encounters the canon protagonist or replaces them is up to you.
2. It must be a 'regain humanity' story. You will have to research Regnier to understand, but bare bones, he traded his soul for power and through events, abandoned his humanity and set out to destroy it. For me, nothing is better than having a good villain have a redemption.
3. Regnier must regain his power, and I don't mean what he had with the Ancient Heart powering him, I mean as a leader. He ruled an entire country of orcs and ogres with dark elves and liches loyally serving him as well. While he is basically a one man army on his own, he knows the benefit of having an army himself. So wherever you send him, he must either conquer a country or somehow come into power through other means, but he must at some point regain a country to rule.
4. This one is optional, but recommended. A love interest for Regnier. He was once a married man and even after he became what he now is, his wife, to her dying breath, loved him. It wouldn't be too out there for him to discover how to love again, especially with him regaining his humanity.
Well, that's about all I have for this. I do recommend playing the Kingdom Under Fire games before trying this out, but watching them on Youtube and then researching them also works.