Well, in 'kaneki crossover death note fanfiction', a possible concept is the way their different worlds collide. Kaneki comes from a world full of ghouls and the CCG, and Light is in a world where he's using the Death Note to change society. If they were to meet, it could lead to some really intense power struggles. Also, the idea of how their respective allies and enemies would react to the crossover is quite fascinating. Kaneki's friends from Anteiku might be completely bewildered by the Death Note, and Light's accomplices might see Kaneki as a new threat or a potential tool.
Well, in scp death note crossover fanfiction, a cool concept is the clash of different power systems. The SCP entities have their own unique and often bizarre abilities, and when combined with the Death Note's ability to kill just by writing a name, it creates a really chaotic and interesting scenario. Maybe some SCPs would try to find a way to nullify the Death Note's power or use it to their own advantage in their never - ending pursuit of chaos or control.
A cool crossover idea is if the Shinigami from the Death Note world are interested in the chakra system in Naruto. They might make deals with ninjas, offering them the power of the Death Note in exchange for their chakra or some other valuable things. And also, imagine if Sasuke from Naruto was in the Death Note world. His desire for power and revenge could be redirected in a different way with the existence of the Death Note. He might see it as a tool to take down his enemies more efficiently.
Another possible antagonist could be the CCG in the 'Tokyo Ghoul' universe. If they were to somehow cross paths with the 'Death Note' world, they might see the power of the Death Note as a threat and try to take it. This would put them in direct conflict with both Kaneki and Light, as Light wouldn't want to lose his tool for 'justice' and Kaneki wouldn't want the CCG to gain more power to hunt ghouls. So, in this complex crossover situation, the CCG could end up being an antagonist.
One interesting concept could be Naruto getting his hands on the Death Note. Imagine how his ninja values would conflict with the power of the Death Note. He might be tempted to use it for what he believes is justice in the ninja world, but his sense of right and wrong within his own moral code would be put to the test.
A crossover with 'Fullmetal Alchemist' could also be fascinating. Maybe Edward Elric discovers the Death Note in his search for the Philosopher's Stone. He would be conflicted because his moral code as an alchemist goes against using such a tool for killing, yet the power it offers could potentially help him achieve his goals in a different way.
Well, some OCs in Death Note fanfiction could be a psychic who can sense the presence of the Shinigami. This psychic might be drawn to the chaos that the Death Note is causing and try to use their powers to stop it. There could also be an OC who is a member of an underground organization that has been secretly studying the Death Note for years. They have their own motives, maybe to gain power or to prevent the wrong people from getting their hands on it. And an OC as a street - smart kid who stumbles upon the Death Note and has to make a choice between using it for personal gain or trying to destroy it, which would add a whole new perspective to the story.
Well, perhaps a concept is the power dynamics. If Harry is death in this crossover, he would likely have a great deal of power. In Kuroshitsuji, power is a major theme, especially with Sebastian's demonic powers. Harry's power as death could either clash or complement Sebastian's. This could lead to some really intense and unique storylines where the characters are forced to navigate around these two powerful forces.
One possible plot could be that Light Yagami discovers the existence of demons from the Inuyasha world. He might see them as a new type of 'evil' to be eradicated. He could start using the Death Note on demons, which would draw the attention of Inuyasha and his group. Inuyasha would initially be confused about these strange deaths and then realize that a human is causing them. This would lead to a conflict as Inuyasha believes in slaying demons in a more 'honorable' way and not through this strange notebook's power.
One interesting concept could be how Harry Potter's new role as the master of death changes the power dynamics in the wizarding world. For example, it might make him more feared or respected by other wizards.
One idea could be an evil Kaneki crossover with the world of 'Attack on Titan'. Kaneki's unique kagune abilities could be a new form of weapon against the Titans. He might start off as an experiment by the Marleyans similar to how he was experimented on in the original Tokyo Ghoul story. Another idea is a crossover with 'Fullmetal Alchemist'. Here, Kaneki's struggle with his inner ghoul side could be paralleled with the Elric brothers' search for the Philosopher's Stone to regain their bodies. He could be seen as a new type of chimera in this world.