Well, in such a fanfiction, there could be a whole curriculum at the Pokemon transformation school. Maybe they teach about the history of Pokemon transformation, and the different types of energy needed for each transformation. There could be a group of misfit students who struggle with transformation at first but then discover a unique way to do it and become the heroes of the school.
Often, there would be a main character who has a special ability or potential for Pokemon transformation that they are not fully aware of yet. Alongside them, there could be a strict but fair teacher who plays an important role in their development. There might also be a rival character who is always trying to outperform the main character in transformation - related tasks and challenges.
A strange and rare item could be the cause. Maybe a Vulpix stumbles upon an ancient amulet that has the power to transform Pokemon. Once the Vulpix touches it, the transformation occurs. This amulet could have been lost for centuries and have some sort of legend associated with it.
When Celebi initiates the transformation, it's like a wave of emerald light washes over the target. First, there's a tingling sensation all over the body. Then, the physical features begin to shift. If it's a transformation into a flying - type Pokemon, the back might start to bulge as wings start to form, feathers sprouting out in a flurry. The face would change too, the nose becoming a beak perhaps, and the eyes taking on a different shape and color. Every detail of the transformation can be described in a very tactile way, making the reader feel as if they are witnessing it firsthand. You can also add in the sounds, like a soft whooshing as the transformation energy moves around.
In many fanfictions, Ash's shadow Pokémon transformation can be a really cool concept. It might happen due to some dark energy or a special encounter. For example, he could be influenced by a shadowy force while exploring an abandoned Pokémon facility. This transformation could give his Pokémon enhanced, but more aggressive powers.
He could gain the ability to use Pokemon - specific techniques in combat. For instance, he might be able to use Quick Attack, which would make him move at an incredibly fast speed, much like his own speed - based jutsu in Naruto. His opponents would be caught off - guard by these new moves.
The theme of friendship often pops up. A human - turned - Pokemon might make new Pokemon friends and learn about loyalty and cooperation. Also, there's the theme of finding a way back. Most of these fanfictions involve the character trying to reverse the transformation at some point. They might search for a special item or a powerful Pokemon that can help them.
One common theme is identity. When a character transforms into an anthro pokemon, they often struggle with who they are now. Are they still the same person or something new? Another theme is acceptance. They have to deal with how other pokemon and humans in the story accept or reject their new form.
One popular idea is a trainer being transformed into a Pokémon. This often leads to interesting adventures as they have to adapt to their new form and abilities. For example, they might learn how to use moves like Pikachu's Thunderbolt from a completely different perspective.
Riolu may become more confident. As it transforms, it realizes it has new powers and abilities. For instance, if it gains the ability to sense auras more strongly, it becomes more self - assured in battles and interactions with other Pokemon.