A group of outcasts in the human society could be his allies. They are used to being shunned, so they don't judge Sesshomaru for his past as a demon. They could show him the hidden parts of the human world, like secret passages in the city or places where they can hide from those who would harm them. And together, they could form a sort of family and support system for Sesshomaru.
An old human sage could be an ally. The sage has great knowledge of both the human and spiritual worlds. He could help Sesshomaru understand the reason behind his transformation into a human and guide him on a path to either accept his new form or find a way to reverse it. The sage could also introduce Sesshomaru to other powerful human allies who can protect him from those who might want to harm him in his human state.
A plot could revolve around Sesshomaru's loss of his demonic powers. As a human, he has to find new ways to protect himself and those he cares about. He could start learning human fighting techniques or rely on his wits more. There could also be a plot where he discovers new aspects of the human world that he was oblivious to as a demon, like art or music, and these new interests change his view of humans and the world in general.
I think Jaune could be a likely candidate. He's a main character with a lot of development potential. His insecurities and his strong will to become a better Huntsman could be twisted if he were turned into a Grimm. It would create a great internal conflict as he battles his new nature.
It could be an ordinary person, like a young student who was always curious about the magical world of Faust Alicorns. Maybe they accidentally stumbled upon a magic spell or artifact that caused the transformation.
It could be one of the baby ponies themselves. Maybe the story could be told from their perspective as they experience the world in this new, baby - like state and how they interact with their friends and family who are now taking care of them.
The transformation process itself could be a really interesting part of the fanfiction. It might start with the human experiencing strange glitches in their body, like electrical surges or seeing in infrared. Then, their body would start to change physically, with metal plates emerging from their skin and their internal organs being replaced by Cybertronian components. This transformation could be a painful and confusing experience for the human, but also an exciting one as they discover new powers and abilities that come with their new form.
One possible plot could be that an AI, after some kind of malfunction or experimental procedure, gains human form. In the lemon fanfiction context, perhaps it finds itself in a romantic or sexual situation. It might struggle with new human emotions like love and lust that it has never experienced before as an AI. It could be attracted to a human character and have to navigate the complex world of human relationships while also dealing with its own identity crisis.
Well, perhaps it could be about a powerful human wizard who accidentally casts a spell on the MLP characters and turns them into babies. Then the story might focus on how the other ponies in Equestria have to take care of these baby versions and try to find a way to reverse the spell.
Maybe there is a scientist or an inventor who becomes Percy's ally. This person could be creating new weapons or gadgets that Percy uses in battle. Their alliance could be crucial in giving Percy an edge in the fight. For example, the inventor might create a special type of grenade or a device that can jam the enemy's communication lines.
He could be a race car driver in the human world too. Maybe he'd start from a small town, with a big dream of making it in the racing circuit. He'd have to deal with sponsors, mechanics, and the media, just like in the movie but in a more human context.
Maybe a kind-hearted storyteller. They have the ability to communicate with the animals in the Lion King world through their stories. The animals are fascinated by the human's tales and the storyteller uses this to bring peace and unity among different animal groups, especially during times of conflict. They could also use their stories to inspire Simba to be a better leader.