*OCs are explicitly stated by fanfiction.net's rules to be disallowed in major roles in fanfiction, especially when paired with another main canon character.
*Differentiate between dub and sub when you write; do not use Japanese names and dub characteristic traits. It is jarring.
*Proper grammar and spelling is always appreciated, there are many betas on this site that will easily read a fic over for you so there is no excuse to type like you do not understand your own language.
*YGO Abridged is amusing but the mechanics of that world do not transfer over to the actual show. Using the phrase "a children's card game" in your fic, if for anything but satire or a joke, is inexcusable. If you do not understand how the world of YGO functions, just stay away from the topic altogether. The people who do will thank you.

The three biggest players in fanfiction that do not get treated like actual characters from the show:
Atem\Dark Yuugi
Kaiba Seto
Katsuya Jonouchi

The thing most often forgot when writing out these three males is their pride. Pride is a big determining factor between duelists and these three men have the most of it. Their pride will disallow them from doing things such as but not limited to:

Using pet names.
Asking for help with their problems.
Moving in with each other for no reason.
Walking away from a duel.
Spouting off sentimental dribble every other sentence for no reason other than that "you make me really happy".
Wanting to kiss and snuggle and hug in public.
Wanting to kiss and snuggle and hug in private when the moment is not right.
Admitting they were wrong about something.
Getting help for their problems.
Going on a tangent about their long, dark and emotionally scarring childhoods.
Being clingy.
Giving up on or stopping hate for someone that they have hated throughout the show for little to no reason at all.
Trusting someone blindly.
--In the case of Jonouchi and Atem only; bashing any one of their friends for no reason at all, this especially includes Anzu. Please keep your bias out of your fic.