I'm not sure specifically what 'Cap deage' means. It could be a very specific term, a misspelling, or something relatively unknown. It might be a proper name, a local term in a certain area or a very niche concept.
To be worthy of Mjolnir in this fanfiction, Harry could have a journey of self - discovery. He realizes that his power as a wizard is not just about defeating Voldemort, but about protecting all beings, whether they are wizards, muggles or Asgardians. He could start to train in Asgardian ways of combat and magic, learning their values of honor and courage. Through this process, he gradually becomes someone who Odin or Thor would see as worthy of wielding Mjolnir.
I don't have enough information to say exactly who Cap'n Kathy is. She could be an original character created by the fan fiction writer. Maybe she's a pirate - the 'cap'n' part could suggest that - who has some connection to the wizarding world of Harry Potter.
Yes, in many fanfictions, Spider - Man can be seen as worthy of Mjolnir. His sense of responsibility, self - sacrifice, and heroism are qualities that could potentially make him worthy. He's always looking out for the little guy and putting himself in harm's way to save others.
Yes, there are likely to be such fanfictions. In the world of fanfiction, creators often like to mash up different fictional universes. Combining the magical world of Harry Potter with the powerful hammer Mjolnir from Norse mythology (popularized in the Marvel universe) can lead to very interesting and creative stories.
There are likely fanfictions where Naruto has Mjolnir. Fanfiction is a realm of infinite creativity, and combining these two elements is not unheard of. It could make for a fascinating read. Naruto's character, with his strong will and growth throughout the series, could be a great fit for the idea of being worthy of Mjolnir. And the addition of the hammer's power to his ninja abilities would create a whole new set of adventures and challenges for him to face.