One common theme is the power struggle. In 'alien vs predator x reader fanfiction', there's often a fight for dominance between the aliens and predators, and the reader gets involved in some way. Also, the theme of adaptation is prevalent. The reader has to adapt to the harsh and strange environments created by these two species. For example, in many stories, the reader has to learn how to avoid the acidic blood of the aliens or the advanced hunting techniques of the predators. There's also the theme of friendship or alliance in some cases, where the reader forms an unlikely bond with either an alien or a predator against a common enemy.
One interesting plot could be Ash somehow getting a power - up that allows him to communicate with Arceus on an equal level. Maybe he discovers a new type of Pokémon energy that gives him this ability. Another plot could be that Arceus decides to test Ash to see if he's worthy of some great power or responsibility in the Pokémon world.
In a fanfic, Ash might have a chance against Arceus. Ash has proven time and again that he can adapt to different situations. He could potentially find a Pokémon's weakness or use some unorthodox strategy. However, Arceus is the creator of the Pokémon world. It has the ability to manipulate reality on a fundamental level. So, on paper, Arceus should win. But fanfics often play with the rules, so Ash could win through some plot - driven miracle.
The Alien in the game has a complex story. It involves their life cycle, from face - hugging to chest - bursting. They are highly aggressive and hunt in packs in the game's setting. Their goal seems to be spreading and eliminating any threats.
One possible plotline could be that the Lake Trio discovers a threat to the world that Arceus is either unaware of or is causing (unintentionally perhaps). So they have to battle Arceus to stop this threat. Another could be that a powerful villain manipulates the Lake Trio into believing that Arceus is a danger and they must fight it.
One popular 'alien vs predator x reader fanfiction' is 'The Encounter'. It has an exciting plot where the reader character gets caught in the middle of a battle between the aliens and predators. Another great one could be 'Surviving the Hunt' which focuses on the reader's struggle to survive in their world.
In Arceus x Silvally fanfiction, a possible plot could be that Silvally, being a synthetic Pokémon, is shunned by many. But Arceus sees its potential. Arceus could use Silvally to bridge the gap between the natural and the artificial in the Pokémon universe. They might embark on a journey together, facing challenges that test their bond and the very fabric of the Pokémon world's existence.
They could be unlikely allies. Maybe in a world where the Pokémon ecosystem is out of balance, Arceus, the symbol of order, teams up with Silvally, a Pokémon with a complex past. Together, they might restore balance, with Arceus guiding Silvally's actions and Silvally using its strength to carry out Arceus's plans.
For me, the most memorable parts of the Alien story in the game are related to their hunting behavior. They are very sneaky. They can suddenly appear from the shadows or from above. Also, the whole process of their life cycle shown in the game is quite unforgettable. From the eggs lying around waiting for a victim, to the face - huggers attaching to hosts and then the full - grown Aliens emerging. It all adds to the horror and mystery of the Alien's story.
The relationship can be explored through their power dynamics. Arceus is the creator, all - powerful, while Giratina is the banished one, yet has its own great power. Their interactions could start with Arceus trying to control Giratina's actions in the fanfiction, but Giratina resists. This power struggle can then evolve into a more equal relationship as they get to know each other better. For example, they might start to share their views on the Pokémon world and the balance of power within it.