He might use chakra - infused metals. Since in the Naruto universe, chakra can be imbued into objects to give them special properties. Maybe he finds some rare ores from the Hidden Stone Village mines which are known for their strong and durable minerals.
It could have the ability to cut through any jutsu. Naruto's sword might be designed in such a way that it disrupts the chakra flow of a jutsu, allowing it to slice through even the most powerful ninjutsu like the Rasengan or the Chidori.
Another possibility is that Naruto gets the materials as a reward. He could complete a really difficult mission for a blacksmith or a village elder. In return, they give him the unique and strong materials required to make the buster sword. He would then use his own creativity and some basic forging knowledge to shape it into the buster sword.
Naruto could use materials from the Sage of Six Paths' realm. Given his connection to the Sage of Six Paths' power, materials from that realm might be accessible to him. These materials could be something that doesn't exist in the normal ninja world and would give his swords unique properties.
One idea could be that Naruto creates his sword using his chakra. He might infuse it with the power of his Nine - Tails chakra, making the sword have a unique orange glow. This sword could have the ability to cut through any jutsu, like a hot knife through butter.
Well, in most fanfictions, he might use a special kind of wood like elderwood which is often associated with magic in the Harry Potter universe. Maybe he also adds some magical items to it, like a phoenix feather for extra power.
In many fanfictions, Naruto might have a special mentor or encounter a unique training situation that leads him to master the use of the sword.
The story in this fanfic might center around Naruto's motivation for creating the seantent sword. Perhaps he wants to create a weapon that can defeat a new and powerful enemy. He might have to travel to different places in the Naruto universe to find the right components for the sword. And during this process, he could learn more about his own powers and the history of his world.
He could discover it during a dangerous mission in an ancient ruin. Maybe he was exploring an old ninja stronghold and came across the sword hidden away. It might have been protected by traps and guardians, which he had to overcome to obtain it.
Another way is through his experiences. Naruto has faced many powerful enemies and learned from different ninja masters. He could use the knowledge he gained from them. For instance, he could use the forging techniques he learned from Tenten, who is an expert in weaponry. He combines this with his own unique ninja skills. Maybe he adds some of his hair or blood to the sword during the creation process, imbuing it with his own essence, making it a truly one - of - a - kind weapon that only he can wield to its full potential.
Well, in some fanfictions, he might inherit it from an unknown ninja clan. Maybe his parents left it for him and it was hidden until he discovers his true heritage.