The Water Dragon Jutsu could be modified to carry other elements within it. For example, the user could infuse lightning chakra into the water dragon. So when the dragon attacks, it not only hits with the force of water but also delivers electric shocks. This would be a great new battle strategy as it combines two different elements for a more powerful and unexpected attack.
Maybe in the fanfiction, the Water Dragon Jutsu has been corrupted by an evil force. Naruto and his friends have to find a way to purify it. They might need to travel to an ancient water temple where they face various trials and battles with dark water creatures that were created due to the jutsu's corruption.
One cool jutsu could be the Water Spiral. Naruto would spin water around his body at a high speed, creating a protective and offensive spiral. Another could be the Water Mirror Clone. He creates clones made of water that can reflect attacks back at the enemy. And there's the possibility of the Water Tsunami, where he summons a huge wave of water to overwhelm his foes.
There could be a jutsu that allows for instant teleportation across long distances. This jutsu might be a new discovery in the fanfiction world, perhaps created by a character who has been experimenting with space - time ninjutsu. They might use it to quickly get in and out of battles or reach far - off places in a blink.
Jiraiya could be one. Although he is known more for his fire and earth - based jutsu, he has vast knowledge and could guide Naruto in using water affinity in unique ways. Another could be Kisame. He is a master of water jutsu. His skills with water manipulation are top - notch, and he could teach Naruto some really powerful and advanced water techniques.
Maybe Sasuke. Although they are rivals, they also have a deep bond. Sasuke might have come across a unique jutsu during his travels and decide to teach it to Naruto so that they can both become stronger and better protect their village.
He might learn a time - traveling jutsu. This would be really cool as it could allow him to go back and change certain events in the Naruto world, or gain knowledge from the past to use in the present battles.
A 'Solar - Flare Rasengan'. Naruto could combine his wind - style chakra with some kind of solar - based energy he discovers. This jutsu would be like a super - charged Rasengan that emits a blinding light as well as powerful wind - based damage.
There might be a fanfiction where the Water Dragon technique is combined with some other elements or ninjutsu in a creative way. For example, a fanfic could show a character fusing the Water Dragon with lightning to create a more powerful and electrified version of the attack. It could also involve a story of rivalries between different ninja clans who all want to master this new form of the Water Dragon jutsu.
He could potentially learn the Flying Thunder God Technique. It's a very powerful jutsu that Minato was famous for. Naruto's already fast with his Sage Mode and Nine - Tails Chakra, and this would make him even more formidable in battle.