The author might use various methods. For example, they could keep key information from Harry's past hidden from him. Maybe they show his normal wizarding life at Hogwarts, with no signs of his heir status, so that when small hints start to appear, it creates mystery. His friends might not notice anything different either, which adds to the enigma.
Well, often in such fanfics, the author will have characters around Harry act as if they know nothing. So, when Harry starts to have strange dreams or unexplained abilities, it makes the reader wonder. The author may also introduce new characters or ancient prophecies that seem to be related but are not fully understood, thus building the mystery around his heir identity.
A possible plot twist could be that the heirship is not what it seems. Maybe it's not related to a noble wizarding family but to an ancient, forgotten magic. Another twist could be that someone else has been manipulating events to make Harry think he's the heir when he's not, or vice versa.
In the fanfic, it might be that the people around Harry treat him as an ordinary person most of the time. So, he doesn't get the sense that he is a hero. For example, his friends might joke around with him and not give him the 'hero - treatment', which makes him oblivious to his heroic status.
Well, it depends on the specific fanfiction. Some authors might make Harry the heir as part of a grand plot. For example, they could tie it to an ancient prophecy or a hidden power within the school. This can lead to new adventures and challenges for Harry, as he discovers his new role and the responsibilities that come with it.
It could be that he is constantly compared to other more 'flashy' characters in the fanfic world. Those characters might have more obvious powers or more dramatic backstories. So, Harry, with his more understated heroism, doesn't think he measures up and doesn't realise he is a hero too. He feels like he's just an ordinary person in the midst of these seemingly more extraordinary individuals.
It could be that there are some underlying reasons within the plot of the fanfic. For example, Harry might have some sort of trauma or moral stance that prevents him from competing. Or perhaps he's more focused on other aspects of his life, like exploring magic in a non - competitive way, or building relationships. So he simply chooses not to compete.
It could mean a fan - created fictional story where the character Harry has reached a point of no longer caring about something. Maybe he's been through a lot in the original story context and in this fanfic, he's just given up on caring about certain events, relationships, or goals.
It might also suggest that the Harry Potter franchise, in an official capacity, doesn't really take into account fanfic. The official Harry Potter universe has its own set of stories, lore, and development. Fanfic is a separate realm created by fans for their own enjoyment. So, it's like Harry Potter, representing the official brand, is indifferent to fanfic because it exists in a different sphere of creativity.
The author might describe his shivering. For example, 'Harry Potter was cold, his body shaking uncontrollably as he stood there.'
It makes Harry more complex. He has to deal with the darker side of his new identity. He might become more reserved as he tries to figure out what it means to be the heir of Slytherin.
His relationship with Hermione and Ron would be strained at first. They would be confused and a bit scared. But as they see Harry resist the dark side, they would become more supportive. With Dumbledore, there might be a new level of secrecy and mistrust at the start, but Dumbledore would likely keep an eye on Harry to see how he develops. As for the other students, many would be afraid and avoid him, but some might be curious and try to befriend him to see what it's like to be around the heir of Voldemort.