You can try fanfiction websites like FanFiction.net or Archive of Our Own. They usually have a large collection of Pokemon fanfictions, including those related to Baby Arceus. Just use their search functions to look for it specifically.
Fanfiction about Giratina and Arceus can take many forms. Some may focus on epic battles between them, imagining different scenarios where their powers clash. Others might delve into their creation myths and how they are connected in the fan - created universe. For example, a story could explore how Giratina's banishment to the Distortion World by Arceus affected its personality and its view of the other Pokemon and the world itself.
Redemption is another common theme. Giratina, being banished, could be on a path of redemption in some fanfictions. It might try to prove itself to Arceus or the other Pokemon. This can lead to really interesting character development stories.
Often, protection is a theme. People or other Pokémon in the fanfiction will try to protect the baby Arceus from those who might want to harm it because of its potential power. Also, the theme of growth is prevalent. We see baby Arceus evolving and growing in terms of its powers and understanding of the world.
I'm not sure specifically which ones are the most popular. However, usually, the ones that gain popularity are those that have a really engaging plot. For example, a story where Arceus has to save the Pokémon world in a unique way. Also, if the lemon aspect is tastefully done and adds depth to the relationships in the story, it might attract more readers.
The theme of mystery is quite prevalent. Both Arceus and Giratina are shrouded in mystery in the Pokemon lore. Fanfictions often expand on this, creating stories where trainers or other Pokemon are trying to uncover the secrets behind these two legendaries. For example, stories might revolve around the origin of Giratina's exile and Arceus' true intentions for the Pokemon world. There are also themes of friendship and cooperation, where unlikely allies come together in the presence of these two powerful Pokemon.
Another theme is the power of friendship. Ash's relationship with his Pokemon is central. When he meets Arceus, his Pokemon friends might play a crucial role in the encounter. For example, Pikachu could use its electric attacks to protect Ash if there's any danger during the meeting.
Well, the plot could involve Ash getting transported to a special realm where Arceus resides. Maybe Arceus sees something special in Ash and decides to test him. Ash could be given tasks that are related to saving the Pokemon world from a great danger that only he, with the help of Arceus, can prevent.
One highly regarded story is 'Ash's Arceus Adventure'. In this fanfiction, Ash embarks on a journey with Arceus to stop an evil organization from stealing the essence of all the legendary Pokemon. The story is great because it combines action, mystery, and the unique bond between Ash and Arceus. Another good one is 'Arceus and Ash: The Legendary Bond'. It focuses on how Ash's pure heart and determination attract Arceus, and they work together to heal a sick Pokemon world. The detailed descriptions of the Pokemon and the emotions of the characters make it a top pick. And then there's 'Ash, Arceus, and the Time - Twisting Quest' where Ash travels through time with Arceus to prevent a cataclysmic event that would destroy the Pokemon timeline.