Seeing Naruto's power in fanfiction can greatly influence Boruto's character. It could make him more determined to reach his father's level. He might start training harder and be more serious about his ninja duties.
Boruto might be in awe. He has always known his father as the Hokage, a powerful and respected figure. Seeing Naruto's past full of struggles, loneliness, and determination would make him realize how far his father has come. It could also make Boruto more empathetic towards Naruto and perhaps inspire him to be more like his father in some ways.
It could also be that Naruto sees in Boruto's eye a sign of an emerging danger. The eye might hold a clue to a new enemy or a brewing conflict. Naruto, being the experienced ninja he is, would then start to take precautions and train Boruto more intensively to face whatever this sign in his eye indicates.
One common scenario is Boruto getting to see Naruto in a super intense battle, showing off his amazing jutsu. Another could be Naruto using his power to protect the village, and Boruto watches in awe.
I really liked 'A New Beginning for Momoshiki in Naruto'. This fanfiction takes an interesting turn where Momoshiki is reincarnated in a different form and has to navigate the world of Naruto from a different perspective. It's full of action and also some great character development for Momoshiki. Also, 'Momoshiki and Naruto: Unlikely Allies' is a great read as it focuses on how their powers could combine in unexpected ways.
There are fanfictions where Momoshiki and Naruto interact in unique ways. Maybe Momoshiki has some knowledge that Naruto needs, and they have to negotiate. Their power levels are compared and contrasted. Naruto's ability to use Sage Mode and his chakra reserves are pitted against Momoshiki's alien - like powers. It creates a dynamic where both characters are forced to adapt to each other's fighting styles.
There could be physical changes too. Naruto might have a new form that combines his own features with Momoshiki's. His body could become more resilient, like Momoshiki's, and he might have a different chakra signature. This new form could attract the attention of other villains in the Naruto universe, either out of fear or the desire to steal his power. Moreover, his relationships with other characters like Sasuke could be affected, as they have to adapt to this new Naruto who has absorbed Momoshiki.
For the ninja world in the fanfiction, it might bring a sense of peace as Momoshiki was a powerful threat. However, it could also lead to new enemies emerging, seeking revenge for Momoshiki's death. Naruto might also have to deal with the political fallout, as some villages might see his act as an overstep of power or a sign of aggression.
A Momoshiki fanfiction could focus on his relationship with Boruto in an alternate universe. For example, they could end up as allies instead of enemies. They might team up to face a greater threat that endangers both their worlds. This would involve a lot of character development for both of them as they learn to trust each other.