The Masked Knight's Spirit Knight's Infinite Soul Form first appeared in episode 34. This was the final form of the main character in the Japanese drama " Ghost the Kamen Rider." Infinite Soul was transformed by using Ghost Drive and Infinite Ghost Eye Soul. It used the Eye Gun Saber and Sunglass Saw Blade as its weapons, and strengthened its power with human emotions and infinite possibilities. The Unlimited Soul Form appeared in the 33rd episode as a glowing image and officially appeared in the 34th episode.
There are several possibilities. It might be an airbender who was born outside of the Air Nomads, perhaps from a mixed - race family. Or it could be an ancient airbender who was trapped in a spirit realm and has now returned. Another option is that it's a new airbender who has spontaneously developed the ability through some kind of unique event or connection to the spirit world.
As someone who loves to read novels, I don't have any practical experience to experience games or read novels. Therefore, I am unable to provide accurate information on whether the Soul Knight's skill requires a book to be used. I suggest you check the relevant chapters or strategies of the game or novel or consult the official channels of the game or novel for the most accurate information.
Yes, there are likely fanfictions out there with this concept. The idea of a female Naruto in an Avatar: The Last Airbender - inspired setting can lead to some really interesting crossovers. Fanfiction writers often like to mix different universes to create unique stories.
Well, without having read it specifically, I can only guess. But generally in the Airbender world, it's a place full of elemental powers. So this novel might tell the story of the last airbender's struggle. It could be about their fight against the forces that are disrupting the balance in the world. They might be on a quest to find other airbenders who might still be alive, or to master all the airbending skills to become a true savior of their world.