Given Allister's love for Ghost - type Pokemon which are often associated with the unknown and mystery, and Bea's focus on Fighting - type Pokemon which represent strength and directness, their personalities could clash at first. However, as they get to know each other through their shared love for Pokemon, they would find common ground. Allister might share his insights about the more ethereal aspects of Pokemon battles, and Bea could show Allister how to be more confident in the physical aspects of battling, creating a harmonious relationship in the long run.
In some fanfictions, the theme of discovery is present. They might find a new type of Pokemon or a hidden power within their existing Pokemon. There could also be a theme of mystery, for example, if they encounter a strange phenomenon in the Pokemon world that they need to solve. And of course, the theme of loyalty between them and their Pokemon is often explored, showing how their Pokemon support them in different situations.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). There are often a lot of Pokemon fanfictions there, and you can specifically search for ones involving Bea and Allister. Another option is FanFiction.net. Just use their search function and type in the relevant keywords.
Perhaps a story where Allister is having trouble with his confidence in battles, and Bea decides to train him. She shows him new fighting techniques for his Pokemon, and in return, Allister teaches her how to better understand the more mysterious aspects of Pokemon battles. This way, they both grow as trainers and form a strong friendship that helps them face tougher opponents in the future.
I don't know exactly who Bea Munoz is in this story as I haven't read it. But she is likely the central character around which the ghost story revolves.
I think Grookey is a great starter for the Pokemon Sword story. It has a strong start in terms of its attacks and evolves into a very powerful final form. It can easily handle the early - game battles which are important for progressing through the story.
In Pokemon Sword, Sobble is a great choice for the story. It's cute and has a good evolution line. Its final form, Inteleon, is very powerful and can be quite useful in battles throughout the story. Also, Grookey is a good pick. It evolves into a strong and cool-looking Rillaboom, which can handle many of the challenges in the game's story.
The Pokemon Sobble is really good for the story. It's water - type, which gives you an advantage against certain types of Pokemon you'll face in the story. Then there's Grookey. Grookey is a grass - type, and as you progress through the story, you'll encounter areas where grass - type moves are very useful. And don't forget about Scorbunny. It's a fire - type, and having a fire - type Pokemon is always beneficial in a Pokemon adventure.
Early in Pokemon Sword for story progress, Grookey is an excellent Pokemon to catch. As it evolves into Rillaboom, it gains strong grass - type moves that can be very helpful against the many normal - type and water - type Pokemon you'll face in the beginning of the story. Also, Sobble is a great choice. It evolves into Inteleon, which has high special attack and can take on a variety of opponents with its water - type moves. Wooloo is also good as it's easy to find and can be evolved into Dubwool, a solid normal - type for the early game.