A frequent theme is adventure. They embark on a journey either in the Mushroom Kingdom or the Hidden Leaf Village. They face various obstacles and enemies together. Also, the theme of self - discovery can be present as they learn from each other's cultures and abilities. Mario might discover his inner ninja, and Naruto might learn about the simplicity and fun of Mario's world.
Adventure is also a big theme. The characters embark on new quests in unfamiliar settings. For instance, if Naruto is in the Mushroom Kingdom, he has to figure out how to deal with Goombas and Koopas while still maintaining his ninja skills. And for Mario in the Hidden Leaf, he has to adapt to the more dangerous and stealth - based ninja world. There's also the theme of power, as they combine their unique powers to face challenges.
I think Mario and Hinata would be an interesting pair. Hinata's shy but strong - willed nature could contrast with Mario's always - positive and heroic attitude. And Mario could help Hinata become more confident in this cross - over scenario. Another good pair could be Toad and Shikamaru. Toad's small but brave self and Shikamaru's intelligence would make for an engaging dynamic.
One idea could be Naruto getting transported to the Mario world. He might use his ninja skills to help Mario in his adventures, like using his speed to outrun the Bullet Bills. Another could be Mario somehow ending up in the Naruto universe and trying to navigate through the Hidden Villages using his jumping and power - up skills.
One popular Mario and Naruto fanfiction could be about Mario characters getting Naruto - style ninja powers. For example, Mario using chakra to jump even higher or Luigi being able to use shadow clone jutsu to clean up ghosts more efficiently in the Mushroom Kingdom.
One idea could be that Naruto somehow gets transported into the Super Mario world. He could use his ninja skills to help Mario defeat Bowser in a unique way. For example, Naruto's shadow clone jutsu could be used to create multiple distractions while Mario sneaks up on Bowser.
A possible plot could be that the Super Crown is a magical item that was lost in Mario's world and ends up in Naruto's world. Naruto finds it and when he touches it, it creates a strange energy that attracts Mario. Mario then arrives in Naruto's world to retrieve the Super Crown. At first, Naruto is suspicious of Mario, but they soon realize they have to work together to keep the Super Crown safe from villains in both their worlds who want to use its power for evil.
It could be Bowser who has somehow gained the power of a powerful ninja jutsu. He uses this new - found power to take over both the Mushroom Kingdom and start invading the Naruto world. His fire - breathing ability combined with ninja techniques would make him a formidable foe for Naruto and Mario.
A great plot could involve a new threat that is a combination of the dark forces from both universes. Naruto and Mario find themselves in a strange new dimension where the rules of both their worlds blend. They must learn to trust each other and combine their unique skills. For example, Mario's invincibility star could enhance Naruto's speed and strength during battles, and Naruto's sage mode could help him sense hidden traps in the Mushroom Kingdom like he does in his own world.
A really creative one is 'Naruto and Mario: The Fusion Quest'. This fanfiction has a magical device that fuses Naruto and Mario into one being. This new entity has to use the combined powers of both to stop an ancient evil that threatens both the Mushroom Kingdom and the Hidden Leaf Village. It's a wild concept that makes for an exciting read.