One plot idea could be Ash facing a new and powerful villain who has a vendetta against all the previous Kanto champions. This villain could be trying to rewrite the history of the Kanto region's Pokémon battles. Another idea is Ash having to defend his champion title against trainers from other regions who believe he doesn't deserve it because he's from a relatively small town. A third plot could involve Ash finding a rare and mysterious Pokémon in Kanto that has the power to either greatly enhance his team or put them in great danger, and he has to figure out how to handle it while still being the champion.
Well, an interesting plot could be Ash getting involved in a time - travel related incident in Kanto. He travels back in time to the very first Kanto Pokémon battles and has to compete in those battles with his modern - day Pokémon knowledge and skills. This would create a lot of chaos and also give him a chance to learn more about the roots of Pokémon battles in Kanto. Another plot might be that Ash's champion status is threatened when a powerful and ancient Pokémon awakens in Kanto. This Pokémon is so strong that it challenges Ash to a battle, and if he loses, he will lose his title. Also, Ash could be invited to a special event in Kanto where he has to battle against the spirits of past Kanto champions to prove that he is a worthy current champion.
It could be about Ash achieving the ultimate goal of becoming the Kanto champion. Maybe it details his journey, the battles he had to overcome, and the growth he experiences along the way to claim the title.
A plot could involve Ash finding a time - traveling device during his Kanto journey. He accidentally travels back in time and meets a younger version of Professor Oak. Together, they solve a mystery that has been affecting the Pokemon in Kanto for generations.
One idea could be Ash and Serena exploring a hidden, ancient temple in Kanto. They might discover a new, rare Pokemon species there. Another plot could involve them participating in a unique Kanto - only Pokemon tournament that has strange rules.
One idea could be Ash facing a new, extremely powerful and mysterious Pokémon in the Kalos region that no one has ever seen before. This Pokémon could be the key to a hidden power within the Kalos champion title. Another plot could involve Ash having to team up with a former rival from his past travels to overcome a threat to the Kalos Pokémon ecosystem. Maybe there's a dark organization trying to disrupt the balance, and Ash's unique bond with his Pokémon is what's needed to stop them.
I think Brock and Misty could be main characters too. They travel with Ash in Kanto. Brock with his knowledge of Pokémon care and Misty with her own skills as a trainer could play important roles in Ash's journey to become the champion in this fanfiction. Maybe they offer advice, support, or even join in some of the battles.
One plot idea could be Ash and Iris teaming up to face a new, powerful and mysterious Pokemon threat that no one else can handle. They travel through different regions, strengthening their bond along the way.
Ash can be developed further by showing his insecurities as a champion. Maybe he starts to doubt if he really is worthy of the title, and this makes him train even harder. He could also develop new relationships with other trainers in Kanto, learning from them and teaching them in return. Another way is to show his growth in handling the political side of being a champion, like dealing with the Pokémon League's bureaucracy.
A great plot for 'pokemon kanto journey fanfiction' could involve a group of friends starting their journey together. One of them has a Psyduck that is actually really powerful when it finally focuses. Along the journey, they encounter a strange Pokemon behavior that seems to be related to an old Kanto legend. They have to work together to figure out what's going on. The gym battles are more intense because they have to compete not only against the gym leaders but also against other trainers who are after the same rare Pokemon in Kanto. They also face a villain who is trying to disrupt the balance of the Pokemon ecosystem in Kanto by stealing rare Pokemon and using them for their own evil plans.
One interesting plotline could be Ash encountering a rare and powerful Pokémon that isn't part of the original Kanto Pokédex. For example, a shiny Mewtwo that he has to befriend instead of battle. Another could be Ash getting lost in an uncharted part of Kanto and having to rely on his Pokémon's unique skills to find his way out, like Pikachu using its electricity to create a signal. Also, a plotline where Ash teams up with a group of Pokémon trainers who have different goals but they all learn from each other during their journey.
Well, in an 'ash unknown champion' fanfiction, the plot might involve Ash getting lost in a mysterious region. There, he stumbles upon an unknown champion who is facing some sort of problem, like a group of poachers targeting their rare Pokémon. Ash decides to help the champion, and in the process, they exchange their Pokémon training techniques. As they work together, Ash realizes that there are so many new ways to approach Pokémon battles that he hadn't known before.