In fanfiction, they might go on joint missions together outside of school. During these missions, they face various challenges that force them to trust each other completely. For instance, when they are up against a powerful villain, Izuku might be in a tight spot and Shoto has to use his quirks precisely to save him. This kind of life - or - death situation would strengthen their relationship.
One idea could be that Shoto and Izuku have to team up for a special training exercise that goes horribly wrong. They end up in an unknown part of the forest and have to rely on each other's quirks to survive and find their way back. For example, Izuku uses his One For All to climb tall trees to get a better view, while Shoto uses his ice to create shelters at night.
Todoroki might be another likely character. He has a complex power set and has been through a lot of emotional and physical growth. His struggle to control his two quirks could be a parallel to the control needed for Ultra Instinct. If he can master the balance within himself, it could potentially lead to the awakening of Ultra Instinct in him.
The Ultra Instinct in a fanfiction might also have an impact on the character's growth. It could be a new milestone in their hero journey. Instead of just relying on their existing quirks, they have this new ability to master. This could lead to new relationships and rivalries. Other characters might be in awe or jealous of this new power, which would create more drama and tension within the story.
In a fanfic scenario where Naruto consumes the Rumble Rumble fruit, it would be a huge game - changer for him. His chakra nature could potentially be affected, and he might be able to generate electricity from his own chakra. This new power could help him in battles against stronger opponents. He could send out electric waves to disrupt enemy attacks or even paralyze them. Moreover, it could also change his relationships with other characters as they would have to adapt to his new - found abilities.
Well, clearly Sweetballe and Rumble are the main characters. Sweetballe might be a pony with a kind heart and some special abilities or qualities. Rumble, as a pegasus, is likely to have flying skills and a personality that can either complement or contrast with Sweetballe's.
One possible plot could be that a new character arrives in the Naruto world with the Rumble Rumble Fruit ability. This character could initially be seen as a threat by the Hidden Villages. However, as the story progresses, they team up with Naruto and his friends to fight a common enemy, like a powerful group of rogue ninjas. They use the unique powers of the Rumble Rumble Fruit, which can create and control lightning - like rumbles, to gain an edge in battles.