A very experienced author who has written many successful magic novels could claim this. For example, J.K. Rowling with her 'Harry Potter' series has revolutionized the magic novel genre. She could potentially say this because of her great influence.
You can start by looking on fanfiction.net. It has a large collection of Naruto fanfictions, including many that deal with the Kyuubi claim. Another good place is Archive of Our Own (AO3). It has a well - organized tagging system, so you can easily search for Naruto Kyuubi claim fanfictions.
Well, in the fanfic world, the author might have created a backstory or a set of rules. It could be that Tsunade's family lineage has been clearly defined in a way that excludes her from being considered an Uzumaki. Naruto, being a character within that fan - created world, has to abide by those rules. For example, perhaps her family tree has been traced and it shows no connection to the Uzumaki clan, so Naruto simply can't claim her as one.
A claim in a story is a statement or assertion made by a character or the narrator about something. It can be about an event, a situation, or a person.
I think Fargo takes some liberties with the term 'true story'. It might be based on real events or have elements inspired by reality, but it's likely dramatized and embellished for entertainment purposes.
Once you have the genre, character traits, and plot in mind, start writing. Describe the character's appearance using Crystal Reed as a reference, but also add your own unique touches. Write engaging dialogue and keep the story flowing. Don't be afraid to ask for feedback from other fanfic writers or fans of Crystal Reed's work as you go along.
One implication could be on the power dynamics. If Tsunade was wrongly claimed as an Uzumaki, it might disrupt the existing balance of power related to the Uzumaki clan in the fanfic.
Well, in nonfiction, a claim is often based on facts and research. In fiction, it can be an assertion about a character's emotions or a plot development. It's what drives the story or the argument forward.