How can Naruto obtain the ethereal blade in a fanfiction?

He could obtain it by chance. Maybe during one of his adventures, he stumbles upon an ancient temple and the Dragon Blade is just there, waiting for him to pick it up.

Perhaps it's passed down to him by a mysterious figure. This figure could recognize Naruto's potential and believe he's the right one to wield the dragon blade. The figure might be an old ninja who has been protecting the blade for years and now sees Naruto as the savior of the ninja world who needs this extra power.

Well, perhaps the ethereal blade is a gift from a mysterious sage. It can only be used by those with a pure heart, like Naruto. In the fanfiction, Naruto has to prove his worthiness to the blade by going through a series of trials. These trials could involve facing his inner demons and past traumas. And as he overcomes each trial, the blade's power grows stronger within him.

In fanfiction, Naruto could obtain the Golden Sharingan through a powerful ninja ritual. Maybe a sage or an ancient ninja figure passes on the power to him as a last resort to save the ninja world from a great evil. For example, if there's a threat that only the combined powers of the Uzumaki and Uchiha clans can defeat.

Perhaps he stumbles upon it during one of his adventures outside of the village. It could be in an ancient ruin or something.

Maybe through some kind of magical encounter. For instance, he could stumble upon a portal that leads to a world where the Keyblade exists and be chosen by it. It could be that his strong will and desire to protect his friends are what draw the Keyblade to him.

In fanfiction, Naruto could get the Sharingan through a blood - related connection that is revealed later. For example, it could be discovered that he has some distant Uchiha ancestry that gets activated somehow. Maybe a powerful enemy's attack awakens this dormant Uchiha blood in him, and as a result, he develops the Sharingan. It could also be that a powerful sage or a new character uses their own unique powers to bestow the Sharingan upon Naruto for a specific purpose.

He could obtain it through a strange twist of fate. Maybe during a mission in a dimension where the Harry Potter world and the Naruto world collide, he stumbles upon it. It could be lying in an ancient tomb, and Naruto, being curious, picks it up and unknowingly becomes its master.

In a fanfiction, Naruto might obtain the Rinnegan and Sharingan through a unique encounter. For example, he could stumble upon a dying Uchiha who transfers his Sharingan to Naruto in a moment of desperation. As for the Rinnegan, it could be related to his connection with the Sage of Six Paths. Perhaps the Sage's spirit, seeing the great need in the ninja world, bestows the Rinnegan upon Naruto. It could also be a result of some sort of genetic experimentation gone wrong but in a way that gives him these powerful eyes instead of harming him.

He might obtain it through a special encounter. For instance, he could stumble upon an ancient dragon's lair where the chakra is stored and it bonds with him.