Disclaimer: I do not own the series or any of its characters.
Some of these headcanons might become stories sand there will be time you will vote on which ones will become stories, so stay tuned
-Akiza is actually an incest child and Divine is her real biological father. Before the night he left his family as exile for his powers, he and Setsuko, her mother and Divine's biological sister, had sex. The only reason Hideo thinks she his daughter is because he had sex with Setsuko had sex with Hideo a month after having sex with Divine and Setsuko found out she was a month pregnant. Setsuko didn't tell Divine til she was 6 months pregnant and Hideo was away. Explains Akiza's powers and why he took her in so quickly.
-Dragons actually evolved from humans which is why they are intelligent and many times act like them.
-In the signers' past lives Yusei and Akiza were the signer emperor and empress, Rua and Ruka were their children and Prince and Princess, and Jack and Crow were the uncles and advisors.
-Martha used to be the best turbo duelist in Satellite and had a beast and dragon with Stardust Dragon and Red Dragon Archfiend in her deck, but stop when she started to raise Jack and Yusei and only dueled to win money to raise them. She still has her dragon deck and duel runner, Nightmare Moon, and explains how Jack and Yusei got their dragons in the first place and how they learned to play duel monsters.
-Martha actually has a criminal mark under her right eye, but covers it with make up.
-Carly's parents abandoned her at age 5 not wanting to carry the burden of raising a child. She had lived on the streets for 3 months until she put in a foster home and lived with multiple families. That's why she sees Misty as a sister to her, maybe even a mother.
-Carly got her fortune fairy deck form her mother. It was her mother's first deck, but see it as weak and gave it to Carly. She only keep it because she hoped to prove her mother wrong about the deck.
-Carly still has her fortune lady deck with Aslla Piscu in it. They are less powerful and won't influence her.
-In the future, Carly becomes a successful turbo duelist. She got fired when Angela took over as the editor of the newspaper and replaced her with a less clumsy and more successful journalist. Now she is a famous duelist and has earned a world status and marries Jack not too long after gaining that status. She now has issued a restraining order against all NDC Times newspaper employees as a middle finger to Angela.
-The signers are really children of their signer dragons.
*Stardust Dragon is Hakase Fudo in human form, but does not die in Zero Reverse, instead escaped to the spirit world with his wife and helps and watches over Yusei in his duels
*Black Rose Dragon is Setsuko in human form
*Rua and Ruka are actually Ancient Fairy's and Life Stream's children, but both are always in the spirit world
*Black Feather is Crow's mother
*Red Dragon Archfiend is Jack's father