There's been a rare few fanfics I've read where the original characters weren't there to be specifically perfect and adored. Although it's a shounen-ai fic, I remember being FLOORED by the Weiss Kreuz story "Eyes on Me" because the characters that the author created seemed so real. Some you hated, some were cool, some were so ****ing screwed that you wanted to avoid them at all costs, but they were HUMAN. They had personalities, they fit in perfectly with the established canon.....Wow....After so many stinkers and irritating Mary-Sues, I was in awe. For a non-shounen-ai, probably "The White Dog" came to as perfect an original-characters-added fanfic has ever come in my mind....::sighs:: It was just so wonderful to see original characters written into the story so well.
"Adults are just obsolete children, and the hell with them."
~Theodore "Dr. Seuss" Geisel