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.
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.
If the Soul Knight wanted to place the book in the skill bar, he had to first determine the location of the book. Normally, when a Soul Knight's skill was used, the book would have been occupied.
If the book's position was already occupied, then you would need to unlock it first and then move it to the skill bar. Generally speaking, players could unlock items by completing some missions or obtaining some rewards while playing games.
If the book's position was not occupied, then he needed to find the Soul Knight's skill block and move it to the right place. Generally speaking, it could be done by opening the skill bar and clicking on the person who wanted to move the item and then selecting the "Move to" option.
It was important to ensure accuracy when moving items to the skill bar. If you accidentally move other items or the position of the item is incorrect, it may cause the item to be unable to be used normally.
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.
I'd recommend 'Avatar: The Next Generation'. It takes place a few decades after the end of the original series. It follows the new Avatar, who is a waterbender this time, and his adventures. The fanfiction is full of action - packed battles and also delves deep into the new political situations in the four nations.