One possible reason could be some kind of strange chakra infusion. Maybe he comes into contact with a powerful and mysterious chakra source that mutates his body in a way that causes tails to grow. Another reason might be related to some ancient curse or prophecy. It could also be the result of a new jutsu he attempts that goes wrong and has unforeseen physical consequences.
The Karma Seal can change Naruto's appearance. In some fanfictions, it might give him a more menacing look with strange markings spreading across his body.
In certain fanfiction, Naruto is indeed the Ten - Tails. This could be a really cool concept as it combines Naruto's already powerful nature with the ultimate power of the Ten - Tails. It might lead to stories where Naruto has to struggle with the dark side of such power, or he could use it to bring about a new era of peace in the ninja world. Maybe he would have to face off against old enemies who are now even more afraid of his new - found strength.
Maybe through new jutsu or abilities. The fanfiction could give Naruto some unique power that allows him to communicate or negotiate with the Nine - Tails on a different level. He could use this power to show the Nine - Tails a different perspective, like the potential for harmony between them instead of constant struggle.
Well, initially, Naruto might show kindness towards the Nine - Tails despite it being a powerful and somewhat feared entity. He could try to communicate with it on a deeper level. The Nine - Tails, in turn, might be intrigued by Naruto's tenacity. As time passes, they begin to trust each other more. Naruto may share his dreams and fears with the Nine - Tails, and the Nine - Tails might start to see Naruto as someone worthy of its friendship.
Yes, in some fanfictions, Naruto is often depicted as having a very special connection to the Nine - Tails that goes beyond the normal relationship in the original story. For example, he might be able to fully control the Nine - Tails' power in ways not shown in the canon, or they could have a mental bond that allows for unique forms of communication and cooperation.
A new character could be introduced as the host. This character could be from a hidden clan with a special ability to bond with the Eleven Tails. They would bring a fresh perspective to the story, and their journey of coming to terms with the power of the beast and its implications in the Naruto universe would be an exciting plotline.
One possible consequence could be a change in Naruto's power level. If Hinata can control the seal, she might be able to regulate the flow of power from it, which could either enhance or limit Naruto's abilities.
Perhaps an unknown hermit living in some far - off place. In many fanfics, there are mysterious characters that pop up with unique knowledge. This hermit could have mastered the Reaper Death Seal long ago and sees Naruto's potential, so decides to teach him.
One consequence could be that it changes the power dynamics among the Hyuga clan. Since the Caged Bird Seal was used to control the branch family, its removal might lead to a more equal power distribution within the clan.