Well, his bloodline limit could be something that gives him the ability to communicate with animals in a much deeper way than just the normal ninja skills. He could form alliances with powerful beasts that others can't. Or perhaps his bloodline limit is a time - related power, like being able to slow down time for a short period during battles. This would make him a very formidable opponent. Also, it could be a bloodline limit that allows him to transform into a mythical creature, which would add a whole new dimension to his character and the story.
Perhaps the Hiraishin bloodline in Naruto allows him to access a hidden dimension related to the technique. In this dimension, he discovers ancient secrets and powers that were long forgotten. He then uses these newfound powers, combined with the Hiraishin, to become an even more formidable ninja. This could lead to a whole new arc in the fanfiction where Naruto has to balance his new powers with his normal ninja life.
One plot idea could be that Naruto discovers his angel bloodline during a life - threatening battle. His angelic powers suddenly manifest, like the ability to heal himself and his comrades instantly. Another idea is that the angel bloodline makes him able to communicate with spirits, which leads him to gain new knowledge and skills from ancient ninja spirits.
A really interesting plot could be that the Kyuubi bloodline in Naruto starts to have an effect on his relationships. Some people in the village might be afraid of him now that they know he has this powerful bloodline. On the other hand, some might see him as an even greater asset. Naruto then has to deal with the social implications while also training to control the new powers that come with his Kyuubi bloodline. He could also find out that there are other ninja out there with a similar bloodline from other tailed beasts, and they come together to form a unique group.
Another idea is that the ink bloodline limit could be related to sealing techniques. Naruto might be able to use his ink to create seals on the fly. He could trap enemies within ink seals or use the ink to enhance existing sealing jutsu. This would give him a whole new level of strategic options in battles.
Well, you could create a fanfic around a bloodline limit that combines elements of different existing ones. Say, mixing the Sharingan's ability to copy techniques with the Byakugan's long - range vision. This new bloodline limit could give the wielder an almost unbeatable advantage in battle. Also, a bloodline limit that gives the power to manipulate the elements in ways not seen before, like creating hybrid elements easily.
In a fanfiction, you could have a scenario where an enemy uses a dark form of Bakuton bloodline power. Naruto and his comrades must find a way to counter it. They seek out an old hermit who has some knowledge of the Bakuton bloodline's weaknesses. Along the way, they learn more about the bloodline's connection to other elemental powers in the Naruto world, and how it can be used for both destruction and creation.
One idea could be a story where a character with the Shikotsumyaku bloodline discovers a new and powerful bone - related ability that no one in their clan has ever had before. This could lead to them being both feared and respected within the Naruto universe.
One interesting plot idea could be a story where a new character discovers they have a hidden Kaguya bloodline ability that has been dormant for generations. They struggle to control it at first, causing chaos in their village. Another could be a time - travel fanfic where a character goes back to the era of Kaguya and tries to change the course of history regarding the bloodline. Maybe they want to prevent the spread of the more dangerous aspects of the bloodline.
One idea could be a character having a bloodline that combines Naruto's Uzumaki chakra with Sao's game - like abilities. For example, they could have the Uzumaki's massive chakra reserves which they use to power up unique Sao - style skills in combat, like super - fast sword strikes enhanced with chakra. Another plot idea is a story where the bloodline causes a rift between different factions. Some see it as a threat while others as a new hope for their world. This could lead to all kinds of political intrigue and battles.
One idea could be a story where members of the Organization 13 with different bloodlines form an uneasy alliance to take on a common enemy. Maybe a powerful rogue ninja who threatens the entire ninja world.