His classmates could be his allies. They might be intrigued by his Pokemon - quirk and offer to help him train or use it better. For instance, Ochaco could use her zero - gravity quirk to assist Izuku in some Pokemon - quirk - related training exercises.
Yes, there are likely to be such fanfictions out there. The Harry Potter and Pokemon universes are both extremely popular, and fans often like to combine different fictional worlds in fanfiction. You can try searching on fanfiction websites like Archive of Our Own or FanFiction.net.
One interesting plotline could be Izuku using his Pokemon - like quirk to battle villains in a unique way. For example, he might summon Pokemon - inspired creatures with different powers to counter various villain attacks.
Articuno, Zapdos, and Moltres are quite common. Their elemental powers and the mystery surrounding them make for great fanfiction material. Ash might encounter them during his travels and have to either help them or face off against them in some way.
One of the Legendary Pokemon could be Giratina. Despite its somewhat dark and otherworldly nature, Giratina might be intrigued by Ash's light - heartedness and his ability to make friends with all kinds of Pokemon. Dialga and Palkia could also be part of the harem. Dialga, with its control over time, might see Ash as an important factor in the future of the Pokemon world. Palkia, in charge of space, could be interested in how Ash navigates different regions and spaces in his journey. And don't forget about Ho - Oh. Ho - Oh is a symbol of hope and might see Ash as a bringer of hope in the Pokemon world, thus joining his harem.
Arceus is quite popular. Given that it's considered the creator of the Pokemon universe in the official lore, it often has a significant role in fanfictions. Mewtwo is also very common. Its powerful psychic abilities and complex backstory make it a favorite for fanfic writers to explore. Another popular one is Lugia. With its majestic appearance and its connection to the sea, it's often a central figure in many stories.
There could be a mysterious Pokemon that Izuku discovers early on in the story. This Pokemon could have some sort of special power or connection to Izuku. It could be a key factor in his development as a Pokemon fan and as a hero. The Pokemon might not be fully understood at first, and Izuku's journey to figure out its secrets could be a major part of the story.
There are also fanfictions where Ash catches Rayquaza. This could be set during a time when the sky is in chaos due to some dark energy. Rayquaza is drawn to Ash because of his pure heart and determination. Ash, with his usual courage, teams up with his pokemon to assist Rayquaza in restoring balance. As a result, Rayquaza allows Ash to catch it.