One common theme is the clash of cultures. Naruto comes from a world of ninjas and strict training, while Adventure Time has its own very different and often wacky culture. Fanfictions often explore how Naruto adapts to this new world and how the characters from Adventure Time react to his presence.
In such a fanfiction, Princess Bubblegum from Adventure Time could be in the harem. She's intelligent and powerful, and Naruto's unique skills and personality might attract her. Also, Sakura from Naruto could be part of it. Since she has a history with Naruto and in this crossover, she could be part of the group vying for his attention. And Marceline too. Her cool and edgy nature might be drawn to Naruto's heroic side.
Another possibility is that Adventure Time's Princess Bubblegum could collaborate with Sakura. Princess Bubblegum's scientific knowledge and Sakura's medical and combat skills could lead to some amazing adventures. For example, they could be working together to heal a strange illness that is affecting both the Land of Ooo and the Hidden Leaf Village.
A Boruto time adventure in a Naruto fanfic can be really interesting. It might start with Boruto finding some sort of time - traveling device or jutsu. Once he's in Naruto's time, he may face challenges not just in the battles but also in fitting in. He could interact with characters like Sasuke, Sakura, and Kakashi. His presence might also cause some changes in the timeline, leading to unexpected events that both he and the original characters have to deal with.
There are many alternatives. For example, you can write fanfiction about the adventures of Finn and Jake in new, uncharted lands. Or perhaps create a story about Princess Bubblegum's latest scientific discovery. Another option could be to focus on the relationship between Marceline and Princess Bubblegum and how they interact in different situations.
Well, it could be that Naruto, in a strange new world like Adventure Time, has multiple female characters attracted to him because of his godlike powers. Maybe he teams up with some Adventure Time characters and uses his ninja skills in that wacky world while dealing with his new harem.
One interesting plot could be that Naruto somehow ends up in the Adventure Time universe and attracts a harem of the unique characters there. Maybe he uses his ninja skills to protect them from the various threats in Ooo, like the Ice King. And as he spends more time there, different characters start to develop feelings for him.
Naruto and Finn are often paired. They are both the main protagonists in their respective shows and have a lot of similarities. They are brave, determined, and always looking for adventure. Their combined energy would make for an exciting story.
One idea could be that Naruto and Finn the Human accidentally cross paths in a strange dimension. Naruto could be on a mission to find a new type of chakra source and Finn is exploring the unknown. They initially misunderstand each other and fight. But then they realize they both have a strong sense of justice and team up to defeat an evil force that threatens both their worlds.
Another good one is 'When Naruto Met Marceline'. This fanfiction focuses on the encounter between Naruto and Marceline. Their personalities clash and mesh in interesting ways. The author does a great job of showing how Naruto's positive, can - do attitude affects Marceline, and how her more laid - back, but powerful vampire self influences Naruto. It's full of action, humor, and some really heartwarming moments.