In some fanfictions, like 'Emerald's New Path with Ruby', Emerald starts off as an antagonist but Ruby's kindness makes her question her loyalties. Their interaction is initially tense but then grows into mutual respect.
There is a fanfiction where Ruby and Emerald team up in an alternate universe called 'Emerald - Ruby: An Unlikely Alliance'. In this, they face off against a new, powerful enemy and their combined skills make for an exciting read. It shows how their different abilities can complement each other.
One common theme is friendship. Their relationship often starts as comrades and develops into a deep friendship. Another theme is growth. They help each other grow as individuals, like Emerald learning from Ruby's positive attitude.
One popular Ruby x Emerald fanfiction is 'The Bond Between Them'. It focuses on their adventures together and how they gradually develop a deep connection. Another good one is 'Ruby and Emerald: A New Journey' which explores their relationship in a different universe with unique challenges.
Whether the main characters of Pokémon Special, Ruby and Shafia, will appear after the Emerald chapter is still uncertain. Because the plot and setting of the story are in different versions and authors, it is difficult to determine the specific details and arrangements. However, according to the wishes of the author and editor, if these two characters were fully developed and portrayed in future works, they might appear in the story again.
A great plot could involve a Pokemon that has the ability to travel between the Emerald and Ruby regions at will, causing chaos as it steals rare items. The fanfic could follow the journey of two trainers, one from each region, as they try to track down this Pokemon and return the items. They start off as rivals but gradually learn to work together. The different landscapes and Pokemon of the two regions would add a lot of variety to the story.
One idea could be to have Ruby discover a hidden underwater kingdom that is in danger. She could use her unique skills and powers to save it. Maybe there are new types of sea creatures there that she has to befriend in order to succeed.
Use unique character designs. Instead of the typical trainer look, give your characters distinct styles that are inspired by the Emerald and Ruby regions. For example, a trainer from Ruby could have a more fiery aesthetic in their clothing, while one from Emerald could have a more nature - inspired look.
Ruby could be anyone. It might be a name given to a character in a specific story or just a name of a person in real life who likes to read stories in her own time.
I don't know exactly who Ruby is without reading the story. But she is likely the main character, a person who has some kind of story related to reading in the street during her own time.