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.