One idea could be a character who can transform into solid earth structures, like mountains or cliffs, for both offensive and defensive purposes. This would add a new dynamic to battles in the Naruto universe.
In a Naruto solid transformation fanfic, a character could transform into solid lightning. It's not a typical form of lightning ninjutsu. Instead of just shooting bolts, they become a being made of solid electricity, able to move at incredible speeds and deliver powerful shocks on contact.
Perhaps a fanfic where Naruto's Solid Henge goes wrong and he accidentally creates a bunch of strange and uncontrollable objects. This could lead to a comical adventure as he tries to fix his mistakes with the help of his friends like Sasuke and Sakura.
A unique solid transformation could be one that allows the user to transform into a solid form based on their emotions. For example, if they're angry, they turn into a solid, spiky mass of energy. This would be different from the normal elemental-based transformations in Naruto.
One idea could be to have Naruto characters infiltrate a Metal Gear - like facility. For example, Naruto's shadow clones could be used to distract the guards while Sasuke tries to find and disable the main weapon system, similar to how Solid Snake would operate in the Metal Gear Solid games.
One idea could be Naruto using the Solid Henge to create complex and long - lasting structures for strategic purposes in a battle. For example, he could make a huge fortress that the enemy has to break through, adding an interesting twist to the fight.
One idea could be a trainer who accidentally gets exposed to a strange energy and starts to transform into a Pokemon. They then have to figure out how to reverse the process while also experiencing the world from a Pokemon's perspective.
Well, for animal transformation fanfic, you could have a story where a person transforms into a cat. They would then have to adapt to the feline lifestyle - climbing trees, chasing mice (or toys that look like mice), and napping in sunny spots. Or perhaps a transformation into a dragon. This would involve dealing with the huge size, breathing fire (if it's that kind of dragon), and being feared or revered by the people in the story's world. It could be really cool to write about how the character copes with this new identity.
Another interesting concept is a transformation game within the fanfiction where the characters compete to master unique transformations. For example, Sasuke could be challenged to transform into a form that combines his Sharingan powers with a powerful beast, like a dragon, to gain an edge over his opponents.
One interesting idea could be the unique forms the characters take. For example, Naruto might transform into a giant fox - like monster with even more powerful chakra abilities than his regular Nine - Tails form. Another idea could be how the transformation affects their relationships. Maybe Sasuke would view Naruto differently if he had a more monstrous transformation. Also, the origin of these monster transformations could be explored, like if it was a result of some ancient jutsu gone wrong or a new power that emerged in the ninja world.
In some Naruto fanfics, there are transformations related to the tailed beasts that combine the power of multiple beasts. For example, a transformation that fuses the power of the Nine - Tails and the Eight - Tails, creating a super - powerful form with unique abilities like enhanced speed and strength, as well as the ability to control different elements at once.
Well, perhaps a plot where the character's transformation is tied to their emotions in a very unique way. So, when they're extremely angry, they transform into a powerful and somewhat uncontrollable form, but when they're calm and focused, it's a more refined and strategic transformation. And then there could be a quest in the fanfiction to fully master these different states of transformation.