If they were in a situation where they needed to combine their powers, Naruto's Sage Mode, which gives him enhanced strength, speed, and perception, could work well with Meliodas' Full Counter ability. Naruto could sense incoming attacks and Meliodas could then use Full Counter to send those attacks back with even greater force. Also, Naruto's Nine - Tails chakra could potentially merge with Meliodas' demon power in some way, creating a new and extremely powerful force. It could be like a combination of the raw power of the Nine - Tails and the unique abilities of Meliodas' demon form.
Deku's One For All power could be seen as a sort of super - strong magic in the Fairy Tail universe. It could be that he has to learn to control it in a different way, like using the Fairy Tail guild's training methods. Maybe he'd have to combine it with some form of Fairy Tail magic to make it even more powerful.
If Deku had a quirk in fanfiction, it would likely impact his character development. He might have become more powerful quicker or taken on different enemies. The story could become much more action-packed or focus on different themes.
It could make for a really exciting and unique story. Deku's growth and challenges would be measured in a more structured way, adding a new layer of excitement to his journey.
If Batman had Superman powers in fanfiction, he would be an unstoppable force. He could use his detective skills combined with super strength, flight, and heat vision. Gotham would be a much safer place as he could quickly stop crimes across the city without relying on his gadgets as much. He might even be able to take on more global threats, which would be a huge change from his normal focus on Gotham's underworld.
If Naruto had Superman's powers in fanfiction, he would be nearly unstoppable. His existing ninja skills combined with Superman's flight, super strength, and heat vision would make him a formidable force. He could easily defeat his enemies in the Naruto universe, like Orochimaru or Pain, without breaking a sweat.
If Naruto had Wesker's powers in a fanfic, he would be extremely overpowered. His physical abilities like speed, strength, and agility would be enhanced to a superhuman level. He could probably use his Sharingan (if he still has it in this scenario) in combination with Wesker's powers to anticipate his enemies' moves even better. His Rasengan might also gain new properties, like being able to be launched with the extreme force that Wesker can exert.
In fanfiction, the kiss between Meliodas and Elizabeth can be a very powerful symbol. It can represent not only their love for each other but also the hope for the future of their world. It could be that their love is seen as a force that can bring peace or change things for the better. It's also a way for the author to connect with the readers' emotions on a deeper level, as many readers are invested in the relationship between these two characters.