One interesting concept could be creating an OC who is a half - vampire, half - human and exploring their struggle to fit in both worlds. They might have unique powers that neither vampires nor humans possess.
First, think about your OC's background. Decide if they are a vampire, a human, or something in between. For example, if they are a vampire, consider what kind of powers they have and how they got them.
In some fanfictions, one could be the Sharingan, which gives abilities like seeing chakra and predicting moves. Another might be the Byakugan, with its great vision powers. And the third could be something unique like the Ketsuryugan, which could have powers related to blood manipulation.
Maybe he uses some kind of special jutsu. It could be a new form of his shadow clone jutsu where the clones are able to analyze and then copy the bloodline traits of the opponents they encounter.
In the 'naruto has 3 bloodlines' fanfiction, these bloodlines can have a profound impact on the story. For instance, if one of the bloodlines allows Naruto to communicate with animals in a special way, it could lead to new alliances and ways of gathering information. A bloodline that enhances his ninjutsu in a unique way might make him the target of other villages or rogue ninjas who want to steal his power. And a bloodline that gives him the ability to heal others more effectively could change his role within the village from just a fighter to also a healer, which would completely shift the relationships he has with other characters and the overall direction of the story.
The six bloodlines in the 'naruto has 6 bloodlines fanfiction' could be really diverse. It might start with the Senju bloodline which is known for its great chakra reserves and strong life force. Then there could be a bloodline related to some sort of space - time manipulation, like a new version of the Kamui ability. There might also be a bloodline that gives the user the ability to communicate with animals in a more profound way, similar to but different from the Inuzuka clan's bond with dogs. Since it's a fanfiction, the author has a lot of creative freedom to come up with these bloodlines.
Well, in some Naruto fanfictions, a disease could be used to create a really unique plot. For instance, if a disease was created that specifically targeted the Kekkei Genkai holders. It would force the different clans to work together to find a cure. This would be a huge shift from the usual clan rivalries. Maybe the disease was created by a rogue ninja who wanted to wipe out all those with special bloodlines to gain power for himself.
One interesting combination could be the Uchiha bloodline with the Uzumaki bloodline. The Sharingan from the Uchiha and the massive chakra reserves and sealing abilities of the Uzumaki could create a really powerful Naruto. Another could be the Hyuga bloodline combined with the Uzumaki. The Byakugan's visual prowess along with the Uzumaki's chakra would give Naruto enhanced perception and more chakra to use for powerful jutsu.
In this fanfiction, the Sharingan from the Uchiha clan is an obvious choice. It has so many abilities like the ability to copy jutsu and predict movements. Naruto could become even more of a prodigy if he absorbs it. Also, the Aburame clan's ability to control bugs could be quite interesting. Naruto could use bugs for reconnaissance or even in combat in ways that are different from his normal fighting style. And the Inuzuka clan's connection with animals, if Naruto could absorb that bloodline, he might be able to form a stronger bond with his summons or other animals in the wild.
One common theme is power. Different bloodlines have different powers, and often there are power struggles or characters trying to control or harness their own powers. Another theme is identity. Characters are often trying to figure out who they are based on their bloodline heritage.