One possible plot could be related to a competition. Clair might be desperate to win a major Pokemon tournament. She sees Ash as a big threat, so she betrays him by stealing his Pokemon's special items right before the tournament. This gives her an unfair advantage, but Ash soon discovers what she's done. This betrayal could then fuel Ash's determination to not only win the tournament without his items but also to expose Clair's unethical behavior.
In a fanfiction, perhaps Clair betrays Ash because she believes he's not a worthy trainer. She might think that Ash's methods are too haphazard and that he's endangering the Pokemon world. So, she teams up with an organization that wants to control the Pokemon trainers, leaving Ash feeling abandoned and betrayed. This could lead to Ash having to prove himself even more to the Pokemon community and also having to face Clair in a big showdown later on.
Ash would probably be really hurt at first. He's a very trusting person, so it would be a big shock. He might start to question his own judgment in trusting her.
In such a fanfiction, perhaps Ash betrays his friends for power. He might be lured by an evil organization with the promise of rare Pokémon or ultimate power, and in the process, turns his back on Pikachu and the others.
Well, in many such fanfictions, it could involve Ash being betrayed by Clair perhaps in a Pokémon battle strategy. Maybe Clair teams up with an unexpected rival against Ash, or she might break a promise regarding Pokémon training or a joint adventure.
One plot idea could be that Clair challenges Ash to a special battle where the loser has to fulfill a strange request. For example, if Ash loses, he has to help Clair train a particularly stubborn Dragon - type Pokémon for a month. Another idea is that they team up to explore an ancient, mysterious cave filled with rare Pokémon and hidden secrets about the Pokémon world. Maybe they discover an old prophecy that involves them and their Pokémon.
There could be some relatively unknown authors who write amazing pokemon ash and clair fanfiction. They might not have a large following yet, but their stories are full of creativity. These authors could be those who focus on the emotional aspects of Ash and Clair's relationship, like how they support each other in their Pokemon - training goals, and how they learn from each other. Their stories might not be as flashy as some others, but they have a lot of heart.
One common theme is adventure. Since it's in the Pokemon world, Ash and Clair often go on various adventures together with other characters in the harem. Another theme is friendship. Despite the harem - like relationships, the stories usually emphasize the importance of friendship among all the characters.
One interesting story could be about Ash and Clair teaming up to face a powerful and rare Pokemon. They might have to combine their skills and knowledge to overcome it.
One possible fanfiction could be about a trainer in Pokemon Gold who has a special encounter with Clair. Maybe the trainer is on a quest to prove themselves to Clair and in the process, discovers a rare Pokemon that Clair has been searching for. This could lead to a partnership between them as they explore the Johto region together.
One interesting plot point could be how they handle their different Pokémon - training styles. Ash is more impulsive and befriends Pokémon easily, while Clair is more traditional. Their marriage could be a journey of learning from each other in that aspect. Another could be dealing with family reactions. Ash has his mom and friends, and Clair has her family in the Dragon's Den. How they all react to the marriage and blend their families could be really engaging.
One possible plot could be that Ash and Rukia are somehow transported to a new dimension where they have to work together to find a way back home. Along the way, Ash's Pokemon skills and Rukia's Soul Reaper abilities complement each other in battles against strange new foes.