A more serious fanfic could be set in a post - apocalyptic world that was destroyed by a combined force of villains from both Naruto and Bleach universes. Naruto and Ichigo are the last hopes. They meet and initially clash due to their different ways of fighting and beliefs. But they gradually learn from each other and combine their powers in a unique way to take on the remaining villains and try to restore their worlds.
One idea could be a crossover where Ichigo, with his Soul Reaper powers, is somehow transported to the Harry Potter universe. He meets some of the Arrancar there who have also found their way into this new world. They could be causing chaos, and Ichigo teams up with Harry Potter and his friends to stop them. Maybe the Arrancar are attracted to the magic in the Harry Potter world and want to harness it for their own power.
One idea could be that Naruto characters are summoned as Servants in FGO. For example, Naruto himself could be a Berserker with his never - give - up attitude and powerful chakra being translated into high - level stats. Sasuke could be an Assassin, using his Sharingan to detect and strike enemies stealthily.
One idea could be that Venom somehow ends up in the Naruto universe. Maybe a strange rift in dimensions brings Venom to Konoha. He could initially be seen as a threat, but Naruto, with his ability to see the good in people (or in this case, symbiotes), tries to befriend Venom. This could lead to some really interesting battles and storylines, like Venom helping Naruto against powerful enemies using his unique powers.
A fanfic could be written where Alita is reincarnated in the Naruto universe as a ninja. She retains her combat skills but has to learn how to use chakra. Naruto becomes her friend and helps her adapt. They go on adventures together, facing off against powerful enemies. Alita's unique fighting style would make her stand out among the ninjas, and together they could become a formidable team.
One idea could be that Deadpool somehow gets transported to the Naruto universe. He'd be really confused at first but then start causing all kinds of chaos with his unorthodox fighting style and fourth - wall - breaking humor. Maybe he'd try to team up with Naruto, thinking he could use some of Naruto's cool jutsu in his own battles back home.
One idea could be a crossover where Naruto characters end up in the world of Highschool DxD. For example, Naruto himself could be transferred to the school in Highschool DxD. He might use his ninja skills in the battles against the devils and fallen angels there. His shadow clone jutsu could really surprise the characters in the Highschool DxD world.
One idea could be that Naruto is somehow transported to the world of the Lich King. He might use his ninja skills, like shadow clones, to fight against the undead minions of the Lich King. His chakra could be seen as a strange and new form of energy in that world.
In a fanfic, Dark Naruto could team up with Eragon. Dark Naruto's combat skills and dark chakra could be combined with Eragon's dragon - riding and magic abilities. They could face challenges like an ancient evil that has been awakened and is causing chaos in both their realms. This would lead to interesting battles and character development as they learn from each other.
A third idea could be a crossover where there is a big tournament. Characters from both Naruto and Hotel Transylvania participate. Naruto and his friends use their ninja techniques, and the monsters from Hotel Transylvania use their supernatural abilities. It would be an exciting and unique battle where the two different worlds' combat styles collide.
One idea could be a crossover where Elizabeth Olsen's character (let's say Wanda from the MCU) is transported to the Naruto universe. She could use her powers in unique ways to interact with the ninja world, like using her chaos magic against ninjutsu. Maybe she teams up with Naruto to fight a common enemy that threatens both their worlds.