The plot could be that Ash and Zoe are transported to a parallel universe where Pokemon and Digimon are fused. They have to find a way back home. Along the way, they meet strange hybrid creatures. Ash uses his Pokemon knowledge to try and understand these new beings, while Zoe uses her Digimon knowledge. They face a lot of difficulties, like a powerful fused - creature that is blocking their path. They need to combine their skills and the powers of Ash's Pokemon and Zoe's Digimon to defeat it and find a way back to their own worlds.
Maybe the fanfiction could start with Ash being curious about Digimon after hearing some rumors. He sets out on a journey to find out more and meets Zoe. Zoe is an expert on Digimon. At first, Ash's Pokemon - centric approach and Zoe's Digimon - focused view cause some friction. But then, a dark force starts to threaten both the Pokemon and Digimon worlds. Ash and Zoe realize they need to work together. They start to train their respective partners in new ways, borrowing techniques from each other's worlds. Their combined efforts lead to the defeat of the dark force and also a new - found respect and friendship between them.
One possible fanfiction could be about Ash and Zoe teaming up in a world where Pokemon and Digimon co - exist. They might start off as rivals, with Ash's Pokemon training skills and Zoe's understanding of Digimon clashing. But as they face a common threat, like an evil organization trying to use both Pokemon and Digimon for bad purposes, they gradually learn to work together. Ash could teach Zoe about the bond between a trainer and a Pokemon, while Zoe could introduce Ash to the unique digital world of Digimon.
One idea could be Ash and Kari teaming up to stop a new threat that combines the chaos of the Pokemon and Digimon worlds. Maybe a villain is creating hybrid creatures and they have to use their combined knowledge and skills to stop it.
Their interaction might also involve some cultural exchange between the Pokemon and Digimon worlds. Ash could introduce Kari to Pokemon treats and how to care for Pokemon, while Kari could show Ash some of the unique digital technologies in the Digimon world. They might even exchange stories about their adventures and the friends they've made along the way, which could strengthen their bond and help them work together better.
In this fanfiction, if Ash turns into a pokemon, perhaps he becomes a Charmander. He could struggle with being in a different form. He might have to adapt to the life of a fire - type pokemon, facing challenges like being weak against water - type attacks and trying to find a way to change back while still having adventures with his friends, who now have to protect him in a different way.
Well, it might be that in this fanfiction, Ash is exploring a new and dangerous area in the Pokemon world. He encounters some strange phenomena or powerful wild Pokemon. There could be a situation where he is poisoned or affected by some negative energy. His body can't handle it and he collapses. His friends or Pokemon then have to search for a cure or a way to revive him, which could be the main focus of the story.
Well, in some cases of 'pokemon ash forgotten fanfiction', it could be that Ash gets sent to a different dimension where no one remembers him. He then has to find a way to make people remember and also deal with the new and often hostile environment. He might start from scratch, trying to regain his Pokemon and his status as a trainer all while facing challenges that are unique to this forgotten state.
In certain fanfictions, Ash might die from an incurable disease that he contracts while exploring a new and mysterious region in the Pokémon world. His Pokémon then have to deal with his loss and some might go on a journey to find a way to bring him back. For example, Pikachu could be determined to find a mythical Pokémon that has the power to revive the dead.
Maybe there's a device that can transform Pokemon into Digimon - like forms and vice versa. A young trainer discovers this device and starts experimenting. This causes chaos as the Pokemon in their new forms have different personalities and powers. Along the way, they have to figure out how to control this transformation and use it to stop an evil Digimon who wants to use the device for world domination.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Digimon Frontier Takuya and Zoe Kiss' on their search bars. There might be some great stories there.
There might be a fanfiction where Takuya and Zoe have to save the digital world from a hidden threat that was overlooked in the original story. Their different personalities, Takuya's impulsiveness and Zoe's thoughtfulness, would make for an interesting dynamic as they figure out how to stop the danger.