I think it could be Kakashi. He's always been a bit of an enigma. In this fanfiction, he could be the one who first discovers Naruto's new ability to sing 'Animal I Have Become'. His reaction to it, whether it's amusement, confusion or concern, would be really interesting to explore. And he might also try to figure out how Naruto got this ability and what it means for the future.
Naruto himself would be the most interesting. Just imagine him, with his energetic and determined personality, now having this strange connection to the song. His singing would be so out of character for him, yet at the same time, it could add a whole new dimension to his character, showing a more artistic and emotional side that we haven't seen much of before.
One possible plot could be that Naruto discovers an ancient scroll that has the power to make him sing 'Animal I Have Become'. As he sings, he transforms into a more primal and powerful form, with enhanced speed and strength. He then has to learn to control this new form while also using his singing to defeat a new and dangerous enemy that has emerged in the Hidden Leaf Village.
Personally, I find Kakashi as a wolf to be the most interesting in a fanfic context. Wolves are known for their intelligence and their pack - oriented nature. Kakashi is a very intelligent character, and seeing him lead a 'wolf pack' of his comrades would be really cool. He could use his wolf - like instincts to strategize and protect his pack, just as he does with his friends in the Naruto series.
If you become an animal in this fanfiction, your character could develop new abilities through training. For example, if you're a wolf, you could train to run faster and have better endurance in the wild. You might also learn how to communicate with other animals in the forest, which could be a useful ability for gathering information.
I think Sasuke would be really interesting. He already has a dark and brooding personality, and adding the power of the Magu Magu no Mi would make him even more formidable. He could use the magma to enhance his sword attacks, creating a molten blade or use it to create traps for his enemies. His Sharingan could also be used in combination with the magma powers to anticipate his opponents' moves better and launch more precise attacks.
I think Thor would be the most interesting. If he turned into a large and powerful animal like a dragon, he could breathe fire and fly. His already - impressive strength and combat skills would be enhanced, and he could be a real force to be reckoned with. He could also use his dragon form to intimidate enemies and protect Asgard or Earth in a very different way.
If you become a dog in this Naruto fanfiction, your sense of smell can be a huge asset. You could use it to track down missing ninjas. For instance, when Sasuke leaves the village, your dog -character could pick up his scent and follow it. This would create a new sub -plot where you try to convince Sasuke to come back. Your animal ability to smell emotions in a way could also be used. You might be able to sense Sasuke's inner turmoil and use that knowledge to try and reach him on an emotional level.
Iruka Sensei could be a really interesting interviewee. He was Naruto's first teacher and someone who really believed in him when others didn't. He could talk about what it was like to teach Naruto and the other students, his own experiences as a ninja, and how he feels about the changes in the Hidden Leaf Village over the years.
I think Naruto and Weiss would have some great interactions. Weiss is from a high - class family and is very proper, while Naruto is this rough - around - the - edges ninja. Their clash of cultures could lead to some really funny and also some really deep moments. Maybe Weiss could teach Naruto about the importance of elegance in combat, and Naruto could teach Weiss about the value of hard work and determination from his own experiences growing up.
I think Kakashi would be very interesting too. His experience and wide range of jutsu would be valuable in a zombie - filled world. He could use his Sharingan to copy any unique abilities the zombies might have and use it against them.
Definitely Gaara. His ability to control sand is unique. In the Borderlands 2 setting, he could use his sand to protect his teammates from the various attacks, like from the psychos or the Loader Bots. His transformation into Shukaku could also be a very powerful and visually striking element in the crossover.