Another origin might be a divine or otherworldly influence. Maybe a god or a powerful spirit took an interest in Naruto and bestowed upon him the gift of pure chakra as a means to help him achieve his goals and protect the ninja world.
It could be due to a unique training method. In fanfiction, perhaps Naruto discovered a new way to purify his chakra through intense meditation or some sort of elemental training that no one else has tried before.
One possible origin could be a long - lost kekkei genkai. Maybe Naruto's family had a secret bloodline ability that was suppressed for generations, and now it resurfaces as the red chakra.
It could be the result of some kind of special training. Maybe he met a hermit who taught him a unique technique to perceive chakra in a visible way. For example, this hermit might have had him meditate in a special chakra - rich area and gradually opened his eyes to the world of visible chakra.
It might be a result of some special training or encounter. For instance, if Naruto had a unique experience during a mission or while training with a new mentor, this could have triggered the unlocking of the chakra chains. It could be that he tapped into a new source of chakra or learned a new technique that enabled this ability.
In some fanfics, Naruto's chakra chains could be a result of some ancient Uzumaki clan ability that he discovers. Maybe it was a hidden power within his bloodline all along, and through intense training or a particular encounter, he unlocks this ability to use the chakra chains.
Well, Naruto's pure chakra might give him an advantage in fanfiction by allowing him to perform more powerful jutsus. Pure chakra could be more easily molded and controlled, enabling him to create unique and devastating attacks. For example, he could use it to enhance his Rasengan to a whole new level, making it larger and more destructive.
One possible origin could be a secret scroll he finds. Maybe it was hidden by an ancient shinobi who had the power to summon ravens, and Naruto stumbles upon it during one of his adventures.
In fanfiction, the chained blades could have various origins. One possibility is that they are a family heirloom that Naruto discovers. Maybe they were passed down from an unknown branch of his family. Another idea is that he finds them during a mission in some ancient ruins. The blades could be tied to a long - forgotten ninja clan that once had great power.
One possible origin could be a new type of training he undertakes. Maybe he discovers a hidden scroll that teaches him a unique form of physical conditioning that gives him super strength.
Naruto might also go through an identity crisis. His whole life has been centered around being a ninja with chakra and using powerful jutsu. Losing his chakra could make him question who he is and what his purpose is. He would have to redefine himself and find a new way to contribute to the ninja world. This could be a long and difficult process for him.
One reason could be for protection. Maybe in the fanfiction, there are powerful enemies targeting Naruto's chakra specifically. Minato, as his father, seals it away to keep Naruto safe from those who would misuse his power.