Well, a cool plotline could be that the twin brother has a relationship with a character that Harry doesn't really interact with much in the original series. Say, he becomes friends with a Slytherin who has a different view on the wizarding world. This friendship could bridge the gap between the houses in a way that Harry's relationships in the original story don't. It could also lead to the twin brother having a different perspective on the ongoing conflict between good and evil in the wizarding world.
Obviously, Harry and his twin brother are the central characters. But other popular characters can include Hermione and Ron. They might interact with the twin brother in different ways compared to how they interact with Harry. For example, Hermione might help the twin with his studies more because he has a different learning style. Dumbledore is also often a key figure. He could have different plans for the twin brother, like entrusting him with a special mission that is different from Harry's.
One common theme is loyalty. The twin brother is always loyal to Harry, standing by him no matter what. For example, in many of these fanfics, when Harry is wrongly accused, the twin brother is the first to defend him.
One common theme is the exploration of family bonds. Since they are twins, the fanfictions often delve into how their relationship is different from normal siblings. Another theme could be competition. They might compete with each other in Pokemon battles or in achieving certain goals in the Pokemon world.
You can start by giving her a distinct personality. If Harry is brave and impulsive, she could be more cautious and thoughtful. This would create an interesting contrast between them. Also, give her some unique hobbies or interests, like she's really into ancient runes or potion - making. This will make her a more well - rounded character.
One popular 'ash has a twin brother fanfiction' could be 'The Twin's Adventure'. In this story, Ash and his twin brother embark on a journey together through the Pokemon world. They face challenges side by side, and their bond as twins is explored in depth. Their different personalities lead to unique interactions with Pokemon and other trainers.
One possible plot could be that the twin brother has a very different personality from Naruto. Maybe he is more reserved and studious while Naruto is brash and energetic. The twin could secretly be training in a different type of jutsu, perhaps more focused on genjutsu while Naruto is into rasengan and other offensive ninjutsu. Their relationship might start off rocky as they compete for recognition in the village, but eventually they come to realize they are stronger together and support each other in battles against powerful enemies.
It could also be shown in their magical abilities. Maybe they have a shared magical signature that only they can recognize. This could be used to identify each other in a crowd of wizards or to unlock a special magical object that only responds to their combined presence.
The twin could change a lot. He might be the one who stops Draco from making some really bad decisions. For instance, if Draco was about to follow Voldemort's orders blindly, the twin could convince him otherwise. This would then change the whole course of Draco's actions and how he interacts with Harry Potter and his friends.