Well, his sisters from 'The Loud House' could make an appearance in some way. Maybe they get transported to the Pokemon world too, or they are just part of Lincoln's memories that he draws strength from. In the Pokemon world, he could meet classic Pokemon characters like Ash, Misty, and Brock. They could help him on his journey or be rivals in some Pokemon battles.
There could be some original characters created just for this fanfiction. For example, a young Pokemon trainer who becomes Lincoln's best friend in the Pokemon world. Also, the villains in the Pokemon world such as Team Rocket or other evil organizations could be in the story. And of course, a wide variety of Pokemon themselves are also characters in a sense. They could interact with Lincoln in different ways, some being friendly and helpful, while others being more difficult to deal with.
His sisters could be main characters. For instance, Lori might give him some advice on how to deal with the braces since she's the eldest and has more experience. Or Leni could be there to offer some fashion tips to make him feel better about his new look with the braces.
Perhaps the fanfiction could center around Lincoln getting a special Pokemon that no one has ever seen before. This Pokemon could have some kind of connection to his family back in 'The Loud House'. He then has to protect this Pokemon from various villains in the Pokemon world who want to use its power for evil. Along the way, he makes new friends and has all kinds of adventures.
One great Loud House Lincoln fanfiction is 'Lincoln's New Adventure'. It takes Lincoln on a journey outside of Royal Woods where he meets new friends and has to face some unique challenges. It's really exciting as it shows a different side of Lincoln's character.
It could be an angry neighbor who has always been annoyed by the Loud family's chaos. They see Lincoln as the main troublemaker (even if he isn't) and decide to kidnap him to teach the family a lesson.
Carlota and Lincoln are the main characters. Carlota could be the one who initiates a lot of the action related to the lemons. Maybe she has a special connection to lemons from her family's traditions. Lincoln then gets involved in her lemon - related plans, and their interactions drive the story forward.
One possible fanfiction could be that Lincoln constantly has bad luck in his attempts to get some alone time in the house. For example, every time he plans to have a quiet reading session in his favorite corner, one of his sisters accidentally spills something on him or makes a lot of noise right there. It could also be that his bad luck extends to school, where he always seems to be the one picked on by the teacher for things that are not his fault, like when his classmates play pranks and he gets blamed in the Loud House Lincoln - bad luck scenario.
I think Lori could be paired well with Lincoln. Since she's the eldest sister, she could be mentoring Lincoln in something, like how to deal with high school or relationships. And then there's Stella. If paired with Lincoln, they could have a story about exploring a new part of town and finding some kind of hidden treasure or secret place that only they know about.
There might also be some original characters created specifically for the fanfiction. These could be other humans who know about Lincoln's secret or other supernatural beings that are related to the vampire lore in the story.
On the positive side, it might force his sisters to reflect on their own behavior. If they realize that their actions led to Lincoln ignoring them, they could make an effort to change. And for Lincoln, he might find that he misses his sisters' company after a while, which could lead to a reconciliation where they all learn to respect each other's boundaries better.
One possible plot could be that Lincoln and Nikki are paired up for a school project. At first, they have some misunderstandings and different ideas on how to approach the project. But as they start working together more closely, they discover they have a lot in common. They both like the same kind of movies and books, and this mutual interest helps them to bond. Eventually, they complete the project successfully and their friendship deepens into something more, like a budding romance.