Opposing characters

Question: I have these two characters,one of which is the main protagonist, who have a "remarkably alike yet critically different" dynamic.

My main character's greatest asset is his ability to strategize, think on his feet, and way with words, occasionally crossing into manipulation. However, in the end he is a kind person at the core and has some issues with feeling guilt for his opponents and actively feels reluctant and ashamed over some of his harsher actions despite their necessity. Over the course of the story I plan to have him refine his abilities and defeat his enemies by outsmarting them rather than smashing their faces in.

However, I thought it would be a good idea that once he begins to become comfortable with his prowess, that I introduce a character who can match his mental capacity step for step. I think I can safely label this character an impact character. I want this character to have an off kilter morality, though not necessarily evil. He thinks of the encounters with the main character as one would think of a board game and be has no real reason to care about his "game pieces" which is why he can out match the main character at first.

My problem is that I find these two characters seem to work best when they're in opposition. However, as my story does contain death and violence, I don't want to have to kill off the impact character. I can't think of a way to have him change his mind and switch sides without making him seem out of character. I was wondering if you can give me some advice as to if it would work to have these two characters on the same side. And if it is possible, how their relationship would work out as the way they bring out the best and worst of each other is usually out of the sheer desperation of facing someone who is just as good as you in almost every way.
Thanks for your time.

Answer: You might consider giving these two characters a common interest or goal, so that, although they may argue about how to obtain it, they are forced to work together (perhaps because each has a skill the other lacks).

It sounds as though you want your main character to remain steadfast and the impact character to change. The impact character will then be pressuring the main character to change throughout the story. However, remaining steadfast will turn out to be the right approach that will allow the main character to achieve the story goal. That success will force the impact character to change.

For example, consider the film The Fugative. In that film, a Dr. Kimble is falsely convicted of murdering his wife. He remains steadfastly determined to identify her real killer. Meanwhile, the impact character is a policeman who does not believe that a convicted criminal could possibly be innocent.

The two characters' common interest is justice. The policeman has the resources of the FBI behind him. Kimble has specialized knowledge of the medical system which is needed to track down the killer (who has a prosthetic arm). Throughout the film they have a running conflict as Kimble tries to stay free and find the killer while the policeman tries to catch Kimble and return him to prison.

However, Kimble's steadfastness eventually leads to the real killer and convinces the policeman to change his attitude.

Best of luck.