Saitama would win. He has shown incredible strength with just one punch. His power seems limitless, and in a fanfiction scenario, his simplicity and raw power would likely overpower Jiren's more complex abilities.
One possible plot twist could be that Jiren discovers a way to nullify Saitama's strength. Maybe he finds some sort of energy - draining technique that weakens Saitama over time. Another could be that Saitama holds back for some reason, like he wants to see the full extent of Jiren's power, and in doing so, he gets into a real struggle.
In this fanfiction, Goku vs Jiren is likely to be an epic battle. Goku's power with the Universe's Watch might bring new and unexpected abilities. Jiren, on the other hand, is an extremely powerful opponent. The fight could involve intense energy blasts, high - speed combat, and strategic maneuvers. It might also explore the growth of Goku's character and his newfound power in relation to Jiren's unwavering strength.
In the fanfiction, the plot could develop such that the power of the universe's watch attracts other villains or powerful beings. They might try to steal the watch from Goku during his battle with Jiren. This would add a new layer of complexity as Goku has to fend off these new threats while still trying to defeat Jiren.
One possible plotline could be that Cell, seeking to prove his superiority, challenges Broly. Broly, in his usual berserk state, accepts without hesitation. The fight could start with Cell trying out his various attacks like the Kamehameha - like Solar Flare and his physical strikes. But Broly's power is just too much and he starts to overpower Cell. However, Cell then reveals a new, hidden ability that he has been developing in secret and the tables are turned for a while.
There probably is. Fanfiction is a vast world where all kinds of ideas are explored. Since Naruto and Jiren are from different anime universes, a fanfiction about Naruto being a fan of Jiren could be really interesting. It might involve Naruto somehow learning about Jiren's power and being in awe of it. Writers could play around with different scenarios like Naruto trying to train like Jiren or even seeking his advice in the fanfiction world.
One possible plot could be that Naruto, through some sort of interdimensional rift, witnesses Jiren's power during the Tournament of Power. He becomes so impressed that he starts to study Jiren's fighting style and tries to incorporate it into his own ninja techniques. This could lead to Naruto facing some resistance from his friends and teachers who don't understand his new fascination, but Naruto persists in his pursuit to become stronger like Jiren.
Another possible ending is that Gohan sacrifices himself to defeat Cell. He could use a self - destructive move that not only takes out Cell but also costs Gohan his life. This would be a very dramatic and tragic ending, but it would also show Gohan's selfless heroism.