He might become withdrawn. Feeling unloved and ignored, Harry could start to keep to himself more, not sharing his thoughts and feelings with his family. He may also become resentful towards the twins, seeing them as the cause of his being neglected, even if it's not entirely their fault.
Harry could react in a very determined way. Instead of wallowing in self - pity, he might focus on his own growth and development. He could start to explore the magical world on his own, trying to find his place and purpose. He may also try to prove himself to his parents, hoping that they will finally notice him and give him the love and attention he deserves. He might be a bit angry at first, but then use that anger as a driving force.
At first, Harry might be really confused. He doesn't understand why his parents are so focused on the twins and seem to forget about him. This confusion could turn into sadness as he misses the love and attention he used to get. As time goes on, he may develop a sense of independence out of necessity. He'll learn to rely on himself more and less on his family. But deep down, he still yearns for their love and acceptance, and this longing might be a constant part of his character in the fan fiction.
Harry might become withdrawn and introverted. Feeling unloved and unwanted, he could start to keep to himself more, spending time alone in his room or exploring the grounds of their home alone, trying to make sense of why his parents seem to favor the twins.
One possible reason could be that the twins might have some special abilities or circumstances that draw the Potters' attention more. Maybe they are more outgoing and seem to need more immediate care or guidance. Another reason could be that there is some sort of miscommunication or misunderstanding within the family. For example, the Potters might think Harry is more self - sufficient when in fact he also needs their love and attention.
It could also be that the Potters are under some sort of magical influence or curse. In the fan fiction world, there could be a dark force at play that makes them see the twins as more important. This force might be manipulating their emotions and perception, leading to the neglect of Harry.
One popular 'alive potters neglected harry' fanfiction might be 'The Forgotten Boy'. In this type of fanfic, the Potters being alive yet neglecting Harry creates a whole new dynamic. It often explores themes of abandonment and Harry's journey to find his place in a world where his own family doesn't seem to care.
Sirius Black could also be part of it. He was Harry's godfather. He might have escaped from Azkaban earlier in this fanfic. He teams up with the Potters to rescue Harry. He could be the one who scouts out the Dursleys' house before the actual rescue operation, using his skills as an Animagus to stay hidden.
Harry might initially feel sad and confused. He could start to withdraw into himself, spending more time alone. Maybe he'll question what he did wrong to be treated this way.
Perhaps there's a plot against Harry by some dark forces, and the Potters believe that only they can protect him properly. They might think that the people who have been taking care of Harry so far are not equipped to handle the new and more dangerous threats. Also, it could be that the afterlife in the wizarding world has some rules or opportunities that allow them to try and get Harry back into their family fold. They could have been given a second chance, so to speak, and are eager to take it.
At first, it might be really awkward. Harry has grown up without them, so he may be hesitant and distrustful. But as time goes on, they start to bond over shared interests or magical abilities. For example, the Potters might teach Harry some family spells that he never knew before.
It could slow down the plot. For instance, if Harry's glasses are constantly malfunctioning, he might miss important clues or signals. This would add more obstacles to his journey of solving mysteries or fighting against the dark forces.
Fanfiction.net is a great place to start. It has a vast collection of fanfictions, including those with the 'alive potters neglected harry' theme. You can use the search bar to look for specific tags related to this concept.