This is a tricky area of copyright law. The general rule is that you can't copyright a story, only the unique expression of that story. So, in other words, you couldn't copyright the story of a little person who goes off in search of adventure and finds a magic ring, but you can copyright The Hobbit
That being said, there are some plot elements and characters that can
be copyrighted. For example, if you wanted to write a story about an alien named "Superior Man" who fights crime on earth and is impervious to everything except kryptonite, you'd probably get a letter from the folks at DC Comics explaining to you why you can't do that.
Without knowing more about the video game elements that you'd like to adapt to your story, I really can't tell whether you're crossing a line or not.