While this is true to a certain degree, the pokemon N is allied with depends on the game version. If you played Pokemon Black, he allies with Zekrom, seeking an ideal world. If you played Pokemon White, as I did, he allied with Reshiram, seeking the truth of what is right.
Although, you can always represent it differently in your own stories. Here, Sulfur chose to have Reshiram appear, since, as you've said, it is technically fan fiction.