A third idea is a fusion of the two worlds. The shinobi villages and Nazarick could form a trade or knowledge - exchange system. Characters from both sides would have to learn about each other's cultures and abilities. This could lead to some really fun interactions, like Albedo trying to learn ninjutsu from Kakashi, or Sasuke being intrigued by the power of the Supreme Beings in the Overlord world.
One idea could be exploring what would happen if Ainz made an alliance with an unexpected race in the New World. For example, forming a bond with a group of dragon lords and how that would change the power dynamics.
One idea could be that Ainz Ooal Gown somehow ends up in the Naruto world. He could start by trying to understand the new world's power system. Maybe he'd initially be mistaken for a powerful jutsu user or a new type of tailed beast. Another plot could involve Naruto's friends being curious about Ainz's undead minions and trying to befriend them, while Ainz is cautious as he doesn't fully trust the inhabitants of this strange new world.
One idea could be that Naruto is somehow transported to the Overlord world and his unique abilities draw the attention of various female characters, leading to a harem situation. Maybe his ninjutsu skills are seen as a form of magic there.
A common plot point is the culture shock. For example, Naruto characters being shocked by the dark and often cruel nature of the Overlord world. Another is the power - up concept. Naruto might gain new powers related to the Overlord's magic system. It makes for some really cool fight scenes.
One idea could be a crossover where Naruto's world and the world of X - 23 from the X - Men collide. Maybe X - 23 is on a mission and accidentally ends up in the Hidden Leaf Village. She has to learn to adapt to this new place with its different culture and ninja ways. Naruto could be intrigued by her and her abilities, and they could team up to face a common enemy.
One interesting plot could be exploring the backstories of the minor characters in the Overlord game world. For example, the lives of the villagers who interact with the powerful overlord character.
One plot idea could be that a character from RWBY gets transported to the world of Overlord. They might have to navigate the power - hungry and often dangerous world, trying to find a way back home while also dealing with the various powerful beings in Overlord. For example, Ruby could end up in the Tomb of Nazarick and have to figure out how to interact with the Floor Guardians without getting killed.
Perhaps Neo could teach Naruto about the concept of the digital world, which Naruto then uses to create a new form of jutsu. Meanwhile, Naruto could show Neo the power of friendship and teamwork in the ninja way, changing Neo's perspective on fighting.
One idea could be that Inari, inspired by Naruto's determination, decides to train hard and develop his own unique ninja skills. He could then join Naruto on a small mission in the Land of Waves and prove his worth. Another plot could be a time - travel plot where Naruto is sent back in time to when Inari was a child and he has to protect Inari and his mother from Gato's men in a different way, changing the course of history in the Land of Waves.
One idea could be that Naruto and Erza are brought together by a powerful magic spell that transports Naruto to the Fairy Tail world. They initially misunderstand each other due to their different backgrounds and abilities. But as they face common enemies, they start to learn from one another. Naruto could teach Erza about his ninja way of never giving up, and Erza could show Naruto the power of magic and the importance of friendship within the guild.