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 aspect of Vegito and Female Gogeta fanfiction could be the exploration of their unique power combinations. In these fanfictions, writers might create scenarios where they team up against a powerful enemy. For example, they could face a new, extremely strong villain that neither could defeat alone. Their combined strength and different fighting styles would make for an exciting story.
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.
One common theme is the power dynamic. Since Gogeta is very powerful, female characters in the fanfiction might either be in awe of his power or strive to match it. For example, a female Saiyan could train hard to be as strong as Gogeta.
Another theme is the exploration of power. Since Gogeta is extremely powerful, in these fanfics, the female character might either be in awe of his power or strive to match it. For example, some fanfics show the female character training hard to reach Gogeta's level of strength.
One common theme is the exploration of their relationship, whether it's a friendship or something more complex. Another theme is the role of Bulma in Gogeta's more action - packed world. For example, in some fanfics, Bulma uses her intelligence to help Gogeta in battles. Also, the idea of how their two different personalities interact is often explored.
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.