Another idea could be focusing on the emotional growth or change of the Overlord character. Perhaps something happens that makes the usually cold - hearted Overlord start to question his or her actions and motives, leading to a more complex and interesting character arc.
A great plot idea might be a crossover within the fanfiction. Maybe the Overlord's world collides with another game world, leading to all sorts of new challenges and interactions for the characters.
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 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.
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 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.
Perhaps an OC that is a merchant trying to make a fortune in the dangerous world of Overlord. They get involved with the various factions by providing rare items, and in the process, they have to outwit both monsters and other shrewd businessmen. Their journey could be filled with both comical and dangerous situations as they navigate the complex political and economic landscape of the game world.
One idea could be the characters from RWBY ending up in the world of Overlord. They might initially be confused and have to adapt to the new, more dangerous environment. Maybe Ruby could mistake some of the Overlord's minions for Grimm and attack, causing a stir among the various factions in the Overlord world.
One idea could be that the Avengers are transported to the Overlord's world. They have to figure out how to get back while also dealing with the power dynamics and strange creatures there. Maybe they form an alliance with some of the non - evil characters in the Overlord world to find a way home.
One idea could be that the demon overlord has a hidden past with Naruto's family. Maybe he was once an ally but was betrayed, and now he's back for revenge while Naruto tries to understand the truth.
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.
Maybe Percy and Albedo could embark on a journey to find a rare magical item that is said to have the power to change the balance of power in the Overlord world. Along the way, they learn about each other's cultures and powers, and their relationship deepens from mere acquaintances to close friends or even something more. For example, Percy could teach Albedo some of his combat tactics, while Albedo could introduce Percy to the complex magic system of the Overlord world.
One idea could be that Saitama from One Punch Man somehow ends up in the world of Overlord. He might be mistaken for a powerful player at first. Since he's so strong, he could easily defeat many of the powerful monsters in the Overlord world, which would cause a stir among the various guilds and NPCs. Another plot could involve the characters from Overlord trying to understand Saitama's power, which is beyond their comprehension as it's not based on magic or typical RPG stats.