In fanfiction, with complete control of blood, Naruto could have a new form of healing. He could control the blood flow to injured areas more precisely, accelerating the healing process. Also, he might be able to detect the presence of enemies by sensing their blood, like a kind of blood - based radar. This would give him an edge in both offensive and defensive situations.
It could be through some kind of ancient training method. Maybe he discovers a hidden scroll that details the art of blood control and spends months or even years mastering it.
Another feature is the character development centered around the blood control ability. Characters may struggle with the morality of using such a powerful and somewhat gory ability. They might have to overcome their own fears or the prejudice of others. In some fanfictions, characters with blood control abilities are ostracized at first because it's seen as something unnatural. So, it makes for really interesting internal and external conflicts.
One popular 'naruto blood control fanfiction' is 'Bloodline's Legacy'. It delves deep into a unique take on blood control abilities in the Naruto universe. The story follows a new character who discovers an ancient bloodline related to blood control and how it changes his journey in the ninja world.
One potential drawback could be the moral implications. Controlling someone else's blood is a very invasive and potentially cruel ability. Naruto, who is known for his kind heart, might struggle with using such a power. Also, it might be difficult to control precisely, and he could accidentally harm allies if he's not careful.
Well, it could be related to some kind of forbidden jutsu he discovers. Imagine Naruto finds an ancient scroll that details a jutsu which allows the user to control blood. He spends time mastering it, and once he does, he can use it to sense the presence of enemies by their blood flow, or even restrict their movements by solidifying their blood inside their veins.
Naruto might also use his blood control to enhance his physical abilities. For example, he could increase the oxygen - carrying capacity of his blood to boost his stamina. Or he could control the blood flow to his muscles to increase their strength momentarily. This would make him an even more formidable opponent in combat, and these applications would make for some really interesting scenarios in the fanfic.
In the fanfiction, it might be that Naruto's poison blood is a result of the Nine - Tails' influence. The Nine - Tails is a powerful and malevolent force. Its chakra could have interacted with Naruto's blood over time, gradually turning it poisonous. This would also add an interesting layer to their relationship. Naruto would not only have to deal with the power of the Nine - Tails but also the consequences of its influence on his blood, which could change how he approaches training and his relationship with the other villagers who might fear his now - poisonous blood.
His blood control ability might also create new alliances or enemies. Allies could see his power as a great asset and join him, while enemies might fear his newfound ability and target him more aggressively. In the context of the fanfic, this would add more twists and turns to the plot. Maybe some characters who were neutral before would now side with Naruto because of his blood control, or some of his old enemies would form stronger alliances against him.
Naruto could develop his water control abilities through intense meditation. By focusing his chakra and mind, he can better understand the nature of water. He may also study the movements of water in nature, such as how rivers flow and how water droplets form. This knowledge would then be applied to his jutsu, gradually improving his control.