Yes, there are some. In some fanfictions, they might start as rivals but gradually develop a deep bond that could be interpreted as love. However, these are often very creative interpretations that deviate from the original animé's more straightforward rivalry theme.
You can try some popular fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions from various fandoms, including Dragon Ball where Goku and Jiren are from. Just use the search function and type in relevant keywords like 'Goku Jiren love' and you might find some interesting reads.
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.
In a 'Goku Saves Naruto' fanfiction, Goku might teach Naruto some of his unique fighting techniques. Since Goku has such a vast knowledge of martial arts and energy control, he could help Naruto become even stronger. For example, he could show Naruto how to better control his chakra using the principles of ki control. And also, Goku's fearless attitude in battle could inspire Naruto to face his enemies more bravely. Goku could also use his Dragon Balls to wish for something that would benefit Naruto or his village, like restoring the damage done by a powerful enemy attack.
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.
It could be someone like Madara Uchiha. He's extremely powerful and his goals are often in conflict with Naruto's. Goku would have to face his Sharingan abilities and his vast array of jutsu.
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.