I'm not sure specifically what the 'shiny smily story' is about as it could be a very unique or personal story. It might be a story full of positive and happy elements, perhaps with shiny things representing something valuable or beautiful and smily characters indicating a cheerful mood throughout the story.
There could be a wide range of characters. It might have a young boy as the protagonist who is always curious about the shiny things around him. And there could be his friends, like a smily little girl who is always optimistic. There might also be some antagonists, perhaps a jealous character who tries to take away the shiny things that bring smiles to others.
Shiny Pokemon are rare in the games, so in fanfiction, they're seen as valuable. Writers often make them high - priced to create a sense of exclusivity. For example, a trainer might have to go through many difficult quests to obtain a shiny Pokemon, and thus it becomes a symbol of great achievement and is priced accordingly in the fictional economy of the fanfiction.
A possible fanfic could be a what - if scenario. What if Shiro had lost her memory completely instead of just parts of it? Ganta would have to find a way to make her remember their bond. This could involve him taking her to all the places in Deadman Wonderland that held special memories for them. It would be a story full of emotion, as Ganta struggles to bring back the Shiro he knows.