Perhaps in the 'pokemon may returns fanfiction', May returns with a newfound ability to communicate with a rare type of Pokémon that no one else can. This could lead to all sorts of adventures as she tries to share this knowledge with other trainers.
One interesting idea could be May's return with a new and powerful Pokémon team. Maybe she has been on a secret training journey and comes back to surprise everyone in a big Pokémon battle tournament.
There might be a fanfiction where May returns to compete in a special Kalos tournament. She has to face tough opponents and also deal with some personal growth along the way. For example, she could learn new battle strategies and form new friendships. This type of story would show her development as a trainer since we last saw her in the Pokemon XY series.
One plot idea could be that May discovers Maxie's plans for Team Magma early on. She then tries to stop him by using her Pokémon skills in a series of battles. Another idea is that Maxie realizes the error of his ways through interactions with May. Maybe he sees her bond with her Pokémon and starts to question his own motives. A third plot could involve May and Maxie having to team up against a greater threat, like a powerful and mysterious Pokémon that is causing chaos in the region. This forces them to put aside their differences and work together.
One idea could be May and Drew getting lost in a mysterious, never - before - explored region in the Pokemon world. They have to rely on their Pokemon and each other to find their way back. Along the way, they discover new Pokemon species and learn more about their own bond.
Well, a plot could involve May finding a magical artifact that accidentally causes TF (transformation) in all the Pokemon in a certain area. As she tries to fix it, she teams up with some of the transformed Pokemon who still retain their intelligence. They go on an adventure to find the source of the magic to reverse the changes. Maybe there's also a sub - plot where May has to prove to some skeptical trainers that these transformed Pokemon are still worthy of care and training.
One idea could be that May enters a special underwater Pokémon race. She has to train her water - type Pokémon like Mudkip to swim faster and dodge obstacles. Another could be that she discovers a mysterious underwater Pokémon cave while swimming and has to explore it with her Pokémon's help. Maybe there's a new type of Pokémon there that's related to water and swimming.
One idea could be Ash and May getting lost in a mysterious new region together. They have to rely on each other's skills and the Pokemon they have with them to find their way out. Another plot could be that they enter a Pokemon contest and cooking competition combined. May focuses on the contest part while Ash tries his hand at cooking for the Pokemon. A third plot might be that they discover a rare Pokemon that is in danger and they team up to protect it from a group of poachers.
Maybe there could be a plot where an evil organization is trying to use a powerful Pokemon, and May and Steven have to stop them. Along the way, May discovers new ways to train her Pokemon with Steven's guidance, and they also learn more about each other's pasts and how they got into Pokemon training.
One idea could be that Kaa discovers a rare Pokemon that only May can communicate with due to her special bond with Pokemon. They then embark on a journey to protect this Pokemon from an evil organization. Another plot could involve Kaa getting lost in a mysterious forest and May using her skills and knowledge of Pokemon to find and rescue him. A third idea is that they enter a Pokemon tournament together where they face many challenges and grow as friends and trainers.
Perhaps Manaphy gets separated from its pod and May, being the kind - hearted trainer she is, helps it. Along their adventure, they encounter a powerful villain who wants to capture Manaphy for its unique powers. May has to use her Pokemon battling skills and her friendship with Manaphy to outwit the villain.
One idea could be that Greninja returns with a new power that it gained during its time away. It could use this power to help Ash in a crucial battle in the Alola region. For example, it might have learned to control water in a more unique way, like creating ice sculptures that can attack opponents.