The plot is crucial. It could be a story about the struggle between Xerneas and Yveltal's opposing powers and how Zygarde tries to maintain the balance. Or perhaps a story where the trainer has to deal with the consequences of the actions of these powerful Pokemon. A plot that keeps you on your toes and makes you want to keep reading is a sign of a great fanfic.
It could be that Serena, being Zygarde's fan, stumbles upon a mystery related to Zygarde's origin. She decides to solve this mystery on her own. Along the way, she has to face various challenges, like dealing with other Pokemon species that are hostile to her search. As she gets closer to the truth about Zygarde, she also realizes her own strength and potential as a Pokemon trainer.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. There are often many talented writers who create stories about these Pokemon. Just search for 'Xerneas Yveltal Zygarde fanfic' in the search bar, and you'll get a list of relevant stories.
Well, in my opinion, a solid team for the Pokemon Shield story would be the following. Firstly, have a Zamazenta. It's a powerful Legendary Pokemon with great stats. Then, add a Centiskorch. It's a Fire - type with high attack power. Next, include a Grimmsnarl. It has good special attack and can be quite a tank. Also, consider a Duraludon. It's a Steel - type which is great for defense against many types. Finally, have a Mr. Rime for its ice - type moves and its unique look. This combination gives you a good mix of offense, defense, and different types to handle various situations in the story.
Well, the duration of the Pokemon Shield story is not fixed. It depends on your playstyle. If you rush through the main quests, it might take around 20 hours. But if you take your time, do side quests, and explore thoroughly, it could stretch to 30 hours or more.
One option is having a team of Zacian, which is a very strong legendary Pokemon. Along with it, you can have a Galarian Slowbro. It has good special defense and some interesting moves. Another great addition would be Centiskorch. It's a powerful fire - type Pokemon that can deal a lot of damage. And for a bit of utility, include a Mr. Rime. It has a good mix of stats and can use ice - type moves effectively.
For the story mode in Pokemon Sword and Shield, Sobble, Grookey and Scorbunny are great starters. Sobble can turn into a powerful water - type, Grookey into a strong grass - type and Scorbunny into a fire - type. They can cover a wide range of types as they evolve.
For the best team in Pokemon Shield story, you should consider having Centiskorch. It's a powerful Fire - type that can dish out a lot of damage. Flapple is also a good option. Its Grass/Dragon typing gives it an advantage against certain types. Boltund is a fast Electric - type that can quickly take down opponents. Grimmsnarl with its Prankster ability can disrupt the enemy's strategy. And Sandaconda can be a great bulky Ground - type to soak up damage.
In Pokemon Shield for the story, you could build a team around Snorlax. It has high HP and can be a tank. Add to that Alcremie which is a Fairy - type with some nice moves. Mr. Rime, an Ice / Psychic type that can be quite strategic in battles. Dubwool, an evolved form of Wooloo, is stronger and can hold its own. And for a fast attacker, Ninjask which is a Bug - type with extremely high speed.
A good team could be Zacian, Rillaboom, Inteleon, Corviknight, Dragapult, and Toxtricity. Zacian is a very strong Legendary Pokemon. Rillaboom is a great Grass - type with powerful attacks. Inteleon is a reliable Water - type. Corviknight can provide good flying support. Dragapult is a fast and strong Dragon - type. Toxtricity can deal with different types of opponents with its dual - type nature.