Well, perhaps Joey is a big fan of the Batfam in the fanfiction. So when he meets them, he fangirls/fanboys really hard at first. Then, as the story progresses, he gets to know them on a more personal level and discovers that they have their own quirks and insecurities just like regular people, which changes his perspective of them completely.
Joey could be an ordinary citizen who just happens to be in the wrong (or right) place at the wrong (or right) time and meets the Batfam. Maybe he's a journalist trying to get a scoop on the Batfam and ends up getting more than he bargained for.
Joey might be really impressed. He could be like a kid in a candy store, wanting to see how all the cool Batfam gadgets work. For instance, when he sees Batman's utility belt, he might be constantly asking questions about what each gadget does.
Well, one possibility is that Joey could be in awe of the Batfam's reputation and skills. He might try to prove himself to them, perhaps by showing off some of his own unique abilities from the Teen Titans. For example, if Joey has some sort of special power like telekinesis, he could use it in a controlled way to gain their respect.
In the 'Spiderman meets the batfam fanfiction', it's possible that Spiderman would be intrigued by the Batfam's gadgets and their more brooding approach to crime - fighting. He might try to lighten the mood a bit. The Batfam, on the other hand, could be impressed by Spiderman's acrobatic skills and his quippy sense of humor. There could also be some interesting interactions between Spiderman and Robin, as they are both younger heroes in their respective universes.
One possible plotline could be that the mind control is used as a way to make Joey and Seto understand each other better. For example, through the mind control, Seto might see Joey's insecurities and the real reasons behind his actions. Another could be that an external force uses mind control on Joey to make him do things against Seto, creating a lot of conflict and drama as Seto tries to figure out what's wrong with Joey and how to break the control.
I think Robin could be very interesting. He's young and full of energy, and in a meeting with the Justice League, he could be in awe of them at first but then prove himself. He might learn new skills from the League members and also show them that the Batfam has its own strengths. For example, his acrobatics and quick thinking could come in handy during a mission, and his interactions with characters like Aquaman or Green Lantern could be really fun to read about.
In some 'itachi meets sarada fanfiction', Itachi could be brought back to life temporarily. He and Sarada might go on a journey together to face a new threat to the village. During this journey, Itachi could act as a mentor to Sarada, teaching her how to handle difficult situations and how to use her Sharingan more effectively.
Another plotline could involve Petunia getting involved in one of the Marauders' adventures by accident. Maybe she stumbles upon them while they are exploring a secret part of Hogwarts and has to work with them to get out of a tricky situation.
One interesting plotline could be Stiles initially being intimidated by the pack but then gradually forming deep friendships. For example, he might start off being scared of their supernatural powers but as he gets to know them better, he realizes they are just like him in many ways, with their own insecurities and desires.
A third plotline could be a love story between Percy and Nancy. They might start off as friends who gradually realize they have deeper feelings for each other. They could go through typical relationship challenges, like jealousy when one of them seems too close to another character, or misunderstandings due to their different backgrounds. Percy's adventurous nature might sometimes clash with Nancy's more methodical approach, but in the end, they find a way to make it work.