A common theme is the clash of cultures. Naruto characters come from a world of ninjas and shinobi values, while Undertale has a very different monster - centered society. Another theme could be the exploration of power. Naruto characters have their own set of jutsu and abilities, and when they are in the Undertale world, how these powers compare to the magic there is often explored. Friendship is also a big theme, as Naruto characters might form bonds with the Undertale monsters.
One possible plot could be that Naruto, while on a mission, somehow gets transported to the world of Undertale. He teams up with Frisk to stop Flowey from taking over both their worlds. Naruto's ninja skills, like his shadow clones, could be used in creative ways in the battles against the monsters in Undertale.
There's also 'Undertale's Influence on Naruto'. This fanfic explores how the concepts from Undertale, like mercy and determination, could impact the Naruto universe. It delves deep into the characters' psyches and how they might change with these new influences. It's a great read for those who like to see crossovers that really make you think about the characters in a new light.
A really interesting plot twist can be when the characters from Undertale end up in the Naruto world and they have to adapt to the ninja way. For example, Sans using his shortcuts in the middle of a ninja battle, which throws everyone off guard. It's unexpected and adds a whole new level of humor and chaos to the story.
One idea could be that Naruto characters end up in the Underground world of Undertale. For example, Naruto with his determination could be seen as similar to the determination trait in Undertale. He might interact with Sans and Papyrus. Naruto could use his shadow clones to confuse the enemies in the Underground. Another idea is that the ninjutsu in Naruto could be combined with the magic system in Undertale. Maybe Sasuke's Sharingan could have an interesting interaction with the soul mechanics in Undertale.
One interesting concept could be the combination of Naruto's ninja abilities with Undertale's unique battle system. For example, Naruto's shadow clones might interact in a strange way with the bullet - hell - like attacks in Undertale. Another concept could be the characters from both universes meeting and forming unexpected relationships. Naruto's friends could meet Sans or Papyrus from Undertale and have to learn to communicate across their very different cultures.
Well, in such a fanfiction, Naruto's godlike abilities would likely make him a very powerful force in the Undertale universe. He could potentially use his chakra powers in unique ways. For example, his shadow clones might be used to confuse the monsters in Undertale. He could also use his Rasengan as a powerful attack against any threats. And his ability to endure and keep fighting would be an asset in the often dangerous situations in the Undertale world.
One of the main abilities would be his chakra control. Naruto has shown great mastery over his chakra, and in an Undertale fanfiction, he could use it for things like enhancing his physical attacks or creating barriers. Another ability is his summoning jutsu. He could potentially summon toads in the Undertale world, which would be a very strange and new concept for the inhabitants there. His Nine - Tails chakra could also give him a huge boost in power, making him able to take on stronger enemies in the Undertale universe.
Well, if Undertale could watch Undertale fanfiction, it could lead to some chaos. For example, Sans might make jokes about the wild scenarios in the fanfics. Papyrus, on the other hand, might be eager to correct any misinformation about himself. And Flowey could use it as a way to manipulate things further, seeing how the fans view the characters and using that knowledge to his advantage in this strange, meta - situation.
Some characters might be amused. For example, Sans would probably make some witty remarks about the fanfiction's plot twists. Papyrus, on the other hand, might be a bit confused at first but then get really excited if he finds a heroic role for himself in the fanfiction.