Well, they could find it really interesting. Maybe they'd be excited to see how the fanfic writers explore relationships between characters in ways that weren't shown in the original GX series. They might also be a bit critical if the fanfic goes against the established personalities of the characters too much.
If Fairy Tail characters were in Yu - Gi - Oh GX fanfiction, they would likely change the dueling landscape. Their strong bonds of friendship would also play a role. Just like in Fairy Tail, they would support each other during duels. For instance, Happy could be a sidekick that gives Natsu some sort of boost during crucial moments in a duel. Their presence would add a more magical and adventurous feel to the Yu - Gi - Oh GX dueling world.
Perhaps they would engage in an epic duel. Jaden with his Elemental HERO deck and Yugi with his Dark Magician - based deck. This duel could be a test of both their skills and a way to exchange ideas about the spirit of dueling.
One great fanfiction idea could be that the Stardust Dragon in Yu - Gi - Oh GX has a special bond with the main character. It could be a story where the Stardust Dragon is not just a powerful card but a sentient being that can communicate with the duelist on a deeper level. They go through various duels together, and the Stardust Dragon helps the duelist understand the true meaning of friendship and the power within.
One idea could be that Naruto somehow gets transported to the world of Yu - Gi - Oh GX. He could befriend Jaden and learn about Duel Monsters. Naruto's skills in combat and his determination could be applied in the Duel Monsters duels in an interesting way. For example, he might use his shadow clone technique to confuse his opponents during a duel.
Aster being hurt in Yu - Gi - Oh! GX fanfiction can open up various storylines. It could be emotional hurt, like losing a very important duel to someone he underestimated. This loss could make him re - evaluate his entire approach to dueling. He might become more withdrawn at first, but then as the story progresses, he could learn from his mistakes. His relationships with other characters like Jaden or Alexis could also change as a result of this hurt. They could either help him through it or distance themselves depending on how the story is crafted.
It's really hard to say. Jaden has his own set of powerful cards and his unique dueling style which is quite aggressive and adaptable. However, Yugi has a lot of experience and his strategies are very deep. So it could go either way depending on how the duel is set up.
A plot could be where the Stardust Dragon gets lost in a different dimension during a duel. The duelist then has to embark on a journey through strange and dangerous worlds to find and rescue it. Along the way, they meet other unique and powerful creatures that are both helpful and harmful.