Ash can be developed by showing his struggle with the Dark Aura. If it starts to influence his decisions, like making him more aggressive in battles or more distant from his friends. He has to constantly fight against these negative impulses, which can show his inner strength. Also, exploring his fear of losing control to the Dark Aura can add depth to his character.
Well, a plot could revolve around a new villain who has the ability to manipulate the Dark Aura. This villain targets Ash because of his strong bond with his Pokémon. Ash then has to explore the origin of the Dark Aura to find a way to defeat this new threat. He might encounter ancient Pokémon along the way that have knowledge about the Dark Aura. And as he delves deeper, he discovers secrets about his own connection to this powerful force.
Often, it's shown as a visible glow around Ash. This glow can be different colors, like a bright blue or a fiery red. It might pulsate when he's excited or focused during a battle.
In many fanfics, Ash's Aura power starts as a latent ability. It might first be triggered by a strong emotion or a life - threatening situation. For example, in some, when facing a powerful and evil Pokemon, his protective instinct towards his team awakens his Aura. Then, as he becomes more aware of it, he starts to train it, often with the help of a mentor figure, like an Aura Guardian.
It could be a fan - made story about Pokemon where Ash has a blue aura. Maybe it involves Ash having some special powers or abilities related to this blue aura in the context of the Pokemon world.
In Pokemon fanfiction, a strong Ash aura could mean many things. It might represent his strong will and determination. Ash has always been a character full of passion for Pokemon battles. His aura could be a manifestation of his unwavering spirit, which can inspire his Pokemon to perform better in battles.
Ash in the fanfiction could learn to use aura by encountering a rare event or artifact that unlocks his potential. Or perhaps he has a series of challenging battles that force him to tap into this ability and refine his skills over time.
One great aspect of Aura Guardian Ash fanfiction could be the exploration of Ash's latent aura powers. Maybe in these stories, Ash discovers he has a much deeper connection to the aura realm than he ever knew. This could lead to him having new abilities and forming unique bonds with Pokémon that are also attuned to the aura.
I'm not sure of a specific one off the top of my head, but you can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just type in 'Ash dark aura' in the search bar and you'll likely find some interesting reads.