One possible fanfiction could be where Ash has to dress as a girl for a mission in the Alola region (Sun and Moon setting). Maybe he needs to infiltrate a group that only allows girls. He would struggle at first with the new appearance but gradually get used to it and use his skills to complete the task.
The plot might involve Ash dressing as a girl due to a bet or a dare. In the Sun and Moon setting, he then has to go about his daily Pokémon - related activities like catching new Pokémon and battling, all while looking like a girl. This could lead to some humorous situations, like other trainers underestimating him. As the story progresses, he could prove that appearance doesn't matter when it comes to Pokémon training.
A fanfiction could focus on Ash Greninja's unique form and abilities. For example, it could tell a story where Ash has to rely on Greninja's special skills to overcome a powerful, mysterious Pokemon in the Alola region. This would show the significance of their partnership in the context of Pokemon Sun and Moon.
One possible fanfiction could be about Ash and Lillie's adventure in the Alola region. Maybe they team up to face a powerful new Pokemon that has been causing trouble. They use their combined skills and the unique bond they've developed throughout their journey in Pokemon Sun and Moon.
One great Ash and Serena fanfiction in the Pokemon Sun and Moon setting is 'A New Adventure Together'. It has a really engaging plot where Ash and Serena meet up again in the Alola region and go on a journey to discover new Pokemon. The author does a wonderful job of capturing their characters and the unique charm of the Alola region.
One common theme is friendship. Ash forms strong bonds with his friends in the Alola region, just like in the series. For example, his relationship with his classmates is often explored more deeply in fanfics.
One possible fanfiction could be where Ash is forced to dress as a girl for a disguise in a Pokemon contest. In this story, his Pokemon have some really funny reactions to his new look.
In some fanfictions, Ash Greninja's moment of saving Ash from a dangerous fall during a battle in the Alola region is really cool. It shows their loyalty and quick reflexes.
In many such fanfictions, the plot might involve Ash's friends suddenly turning against him due to some false accusations or misunderstandings. For example, they could believe that Ash has been secretly working with an enemy group, which leads to his betrayal.
One interesting story could be Ash having a unique adventure in Alola that's different from the main series. Maybe he discovers a new type of Pokémon or a hidden power within his existing Pokémon.