It could show that Percy is more perceptive than the others think. Often in stories, Percy is seen as a bit of a stickler, but this ability to tell the twins apart might indicate he has a deeper understanding of people.
It could be that Percy pays attention to their individual interests within the fanfiction. If one of them has a particular hobby or passion that the other doesn't share as strongly, that could be a clue for Percy. Also, perhaps their interactions with other characters differ slightly. Fred might be more likely to tease a certain character, while George has a different way of relating to that same character.
One implication is the moral dilemma. Percy would have to decide when and how to use such a powerful and invasive ability.
Maybe Harry notices some small physical differences. For example, one of them might have a slightly different hair part or a unique freckle pattern.
In some fanfics, Harry might be able to tell Fred and George apart by their different interests within the story. For example, Fred could be more interested in potion - making experiments that are a bit on the wild side, while George is more into the business side of their joke shop plans. So when they talk about their hobbies or future plans, Harry can distinguish between them. Also, their sense of humor might be slightly different. Fred might crack a certain type of joke more often, like those related to magical creatures in a really absurd way, while George prefers jokes about Hogwarts professors. Through these nuances in their personalities, Harry is able to tell them apart.
One possible way is through their body language. For instance, Fred might stand with his left foot forward more often, while George has a habit of leaning to the right when he's standing still. Harry, being observant, picks up on these little quirks.
It shows her attention to detail. Hermione is known for being observant, and this is another example of that trait.
Another plot point might be that the twins are actually quite amazed that Harry can tell them apart. This could lead to a closer bond between Harry and the twins, and they start to involve him more in their secret schemes because they trust him with this special knowledge.
One interesting plot point could be that Hermione's ability to tell them apart gives her an advantage in a prank war. Since she can identify which twin is which, she can outwit them and turn their own pranks against them. This could lead to a lot of humorous situations and a shift in the power dynamic among the three of them.
Maybe she notices their different mannerisms. For example, George might be a bit more reserved while Fred is more outgoing. Hermione is very observant, so she could pick up on small details like how they talk, their facial expressions when they're joking or serious.
If Merlin can read fanfiction, it means that it can access a vast array of creative ideas that fans have come up with. This might allow Merlin to see different perspectives on the original stories it's related to. For example, if there's fanfiction about Merlin's own adventures that deviate from the traditional tales, it could provide new insights. Also, it might be able to understand the evolving cultural views of the stories through the lens of fanfiction. Fanfiction often reflects the current cultural trends and the desires of the fans, so Merlin reading it could be like getting a real - time update on how the public views the characters and events it's associated with.