Another possibility is to have the characters from the Karakuri Circus be transplanted into the Naruto world. They would have to adapt to the ninja society. The Karakuri puppets could be seen as a new type of weapon or tool in the Naruto world. And the circus performers could use their unique skills to either help or cause trouble in the ninja villages.
The unique machinery and puppet - like creations from Karakuri Circus can be merged with the ninja tools and jutsu in Naruto. For instance, imagine a puppet in Karakuri Circus that can perform a jutsu - like action.
The circus story could involve a musician who comes to perform and meets someone they fall for, and they write or sing a love song about their connection. Or perhaps a character dreams of love while listening to a love song during the circus acts.
Another way is to have Naruto fuse his chakra with someone who has the ability to use Susanoo, like Sasuke. They could create a combined form that has the best of both their powers. The story could detail their journey of learning to work together and master this new form.
One way to combine them could be in a crossover universe. For example, Naruto could be summoned to the world of Highschool DxD through some sort of magical mishap. Gabriel, being an angel in her own right, could be involved in a plot to either help Naruto return home or to use his power for some greater purpose in the Highschool DxD world. Maybe Naruto's unique abilities, like his shadow clones or rasengan, could be seen as strange and powerful in the DxD world, and Gabriel might have insights on how to control or enhance them.
You could also create a story where there is a common enemy for both Naruto and Monster High. This enemy could be threatening both the ninja world and the world of Monster High. So, Naruto and the Monster High gang have to team up. The Monster High students could use their unique powers, and Naruto and his friends could use their ninja techniques to fight this common foe.
Naruto's Rasengan could be infused with the Yuki Onna's ice powers. For example, he could create an Ice - Rasengan that has the destructive power of the Rasengan but also the freezing capabilities of the Yuki Onna's ice. This new jutsu could be used to defeat powerful enemies that are resistant to normal attacks.
They can be combined through a portal concept. A portal opens between the Naruto universe and the Transformers universe, bringing Naruto and Arcee together. Then they can work towards a common goal like saving both universes from a threat that spans across dimensions.
Well, in a Naruto - Game of Thrones fanfiction, you could have the Sharingan (from Naruto) be a rare and mysterious power in the Game of Thrones world. Maybe a character discovers they have this power and it's seen as a sign from the gods. And then, just like in Naruto, there are different levels of power associated with it. This could lead to new alliances being formed as houses try to either control or protect the person with the Sharingan.
In fanfiction, you can also combine their storylines. Say, the plot of 'The Lion King' could be merged with Naruto's journey to become Hokage. Simba's struggle to take his rightful place as king can be paralleled with Naruto's efforts to gain the respect of the Hidden Leaf Village and become its leader. There could be a common enemy that both Naruto and Simba have to face together, something that threatens both the pride lands and the ninja village.
One way to combine Naruto's Rinnegan and DBZ in fanfiction could be through a crossover of power systems. For example, imagine a scenario where a character with the Rinnegan somehow gets transported to the DBZ universe. They could use the abilities of the Rinnegan, like the Six Paths powers, in battles against DBZ characters. The Sharingan's precognition abilities might be compared to the Z - fighters' combat instincts. Another aspect could be in the realm of character development. A Naruto character with the Rinnegan could learn from the DBZ characters' training methods and vice - versa, leading to new power - ups and storylines.