One idea could be exploring an alternate universe where the main characters have different Pokemon partners. For example, instead of Dawn having Piplup as her starter, she could start with a Chimchar. Another plot could revolve around a mysterious new Pokemon that only appears in a long - forgotten part of the Sinnoh region. It could be a Pokemon with unique powers that both the good and bad guys are after. Also, a story about a trainer who travels through Sinnoh backwards, starting from the Pokemon League and working their way to the beginning of their journey, facing challenges in reverse order.
You could write a fanfiction where a group of trainers form an alliance to take on a powerful and evil organization that is secretly controlling the Sinnoh region. This organization could be using Pokemon in cruel and unethical ways, like forcing them to fight until they faint continuously. The trainers would have to gather different types of Pokemon, each with their own special abilities, to stand a chance against this organization. Also, a plot about a Pokemon that has the ability to transform into different forms based on the emotions of its trainer would make for an interesting fanfiction.
A great plot for Pokemon Diamond and Platinum fanfiction could be a time - travel story. A trainer somehow gets sent back in time to the days when the Sinnoh region was first being discovered. They could interact with the ancient people of Sinnoh and learn about the origin of some of the most powerful and mysterious Pokemon in the region. Or, a fanfiction could focus on a Pokemon that has been abandoned by its trainer and how it forms a bond with a wild Pokemon pack. They then go on a journey to find a new purpose in life, facing many difficulties along the way.
A great storyline might involve a group of friends who each have different goals in the Pokemon Diamond and Platinum world. For example, one might be focused on winning all the gym battles, while another is more interested in finding and documenting rare Pokemon species. Their different paths cross and they end up helping each other in unexpected ways.
A plot could revolve around a trainer who gets lost in a mysterious part of Sinnoh that is not on any regular map. In this area, they encounter Pokemon with strange behaviors and new evolutionary forms. The trainer has to figure out how to get back home while also learning about these new Pokemon, perhaps with the help of some local characters who have their own secrets.
One popular theme is the journey of a new trainer in the Sinnoh region, which is the setting for both games. They might face unique challenges and form special bonds with their Pokemon. Another theme could be about legendary Pokemon, like exploring the backstories of Dialga and Palkia in fanfiction. Also, fanfiction often focuses on the rivalries between trainers, adding new twists to the in - game rivalries we see in Platinum and Diamond.
One plot idea could be Darkrai's struggle to fit into the Pokemon world of Pokemon Platinum. Since it's often seen as a menacing and mysterious Pokemon, it could be about it trying to prove that it has good intentions. For example, it might try to protect a small village from other powerful Pokemon threats, all while the villagers are initially afraid of it.
Maybe a fanfic where a trainer's Pokemon gets a strange and unique ability due to an encounter with a mysterious Pokemon in the Platinum and Pearl world. This could lead to all sorts of adventures as they try to understand and control this new power.
One plot idea could be an alternate universe where the main characters' roles are reversed. For example, if in the original the trainer was male, in the fanfiction it could be a female trainer. Another idea is a story focused on the friendship between Pokemon that were rivals in the game, like Piplup and Chimchar.
One idea could be to explore an alternate storyline where the main character fails to stop Team Galactic's initial plan and has to deal with the consequences. Another could be a fanfic centered around a new Pokemon species discovered only in the Platinum region that has unique abilities. Or perhaps a story about a trainer who has the ability to communicate with Pokemon in a more in - depth way than normal trainers and how that affects their journey in the Pokemon Platinum world.
One idea could be a story where Diamond and Platinum are from rival kingdoms. They meet by chance during a diplomatic event. Their initial animosity turns into curiosity as they discover they have more in common than they thought. Eventually, they work together to solve a problem that threatens both their kingdoms, like a dark magic spell that has been cast upon the land.
Cynthia is definitely an interesting character to write about. She's the champion in Sinnoh and has a lot of mystery surrounding her. You can explore her past, her training methods, and what makes her such a powerful trainer. Another character is Barry. His over - eager and sometimes clumsy nature can lead to some really fun and comical storylines in fanfiction.
One popular character to include is Giratina. Even though it's a Legendary Pokemon, it can be given a more complex personality in fanfiction. Maybe it has a reason for being so feared and banished to the Distortion World that goes beyond what is shown in the games. Also, Fantina, the Gym Leader of Hearthome City, with her unique style and love for Ghost - type Pokemon, can be a great addition to a fanfiction. And don't forget about Maylene, the Fighting - type Gym Leader. Her journey to become stronger and her relationship with her Pokemon can be explored in depth.