One way could be through their distinct personality traits. Maybe one twin is more outgoing while the other is more reserved.
In stories, twins can be differentiated by their interests and hobbies. For example, one twin loves reading and the other loves sports. Or, you could show that they have different dreams and goals.
You can tell twins apart in stories by giving them different physical features like a unique birthmark or hairstyle. Also, their clothing choices or accessories can be different.
In the fanfiction, perhaps Harry has a special ability or spell that helps him tell the twins apart. Or it could be as simple as the twins deliberately giving him some secret signs or signals to help him differentiate. Another possibility is that Harry notices differences in their magical auras. Each person's magical aura can be unique, and Harry, being observant, might have detected this difference between the twins.
It could be as simple as their voices. Maybe one has a slightly deeper or higher pitch than the other. Hermione, being intelligent and detail - oriented, pays close attention to these nuances and is thus able to tell them apart.
The main characters are surely Harry and the twins. Harry, being the one who can tell the twins apart, is at the center of this concept. And the twins, whose identities are usually hard to distinguish for others, play an important role as well. Their interactions with Harry are likely to be the main focus of the fanfic.
The unique concept of Harry being able to do what others find difficult is interesting. It gives a fresh perspective on his relationship with the twins.
It shows her attention to detail. Hermione is known for being observant, and this is another example of that trait.
Maybe it's because of his strong observational skills. Harry has been through a lot and has to be observant, so he might notice small differences in the Patil twins that others miss.
Well, in the 'harry can tell the twins apart fanfic', perhaps the way the author describes Harry's thought process is really interesting. He might use his wizarding intuition to distinguish between the twins. For example, their magical auras could be slightly different, and Harry, being perceptive, can pick up on that. It adds an element of magic and mystery to the story.
One great 'Harry can tell the Patil twins apart fanfiction' is 'The Unseen Differences' on FanFiction.net. It delves into how Harry's unique perspective allows him to distinguish between the twins in a really interesting way.
One way is to pay attention to the direction of writing. Some Asian scripts write from top to bottom, while others go from left to right. Also, the complexity and simplicity of the characters can give you hints.
You can look at the art style. Different artists might have distinct ways of drawing characters and scenes.