Often, it's shown through his internal thoughts. The writer might describe Harry having angry and bitter thoughts about his parents when he's alone, like constantly thinking about how they left him to face so many difficulties. For example, he may think 'My parents left me to deal with Voldemort, they didn't care.'
His actions can also display this hatred. He might avoid anything related to his parents. In a fanfic, he could refuse to visit their graves or not want to inherit any of their magical items. This is a more outward sign of his internal hatred.
Often, it's portrayed as a very heart - wrenching moment. Harry may be alone in his dormitory, looking at a picture of his parents and the tears just start to flow. The descriptions might focus on his physical state, like his shoulders shaking and his face contorted in pain.
His thoughts are also used to portray his hatred. The author might write from Harry's perspective, and we can see his negative thoughts about people. He could be constantly thinking about how everyone is out for themselves or how no one really understands his pain, which then colors his view of everyone around him.
He could hate them because he felt they were absent during his difficult childhood. Naruto faced a lot of loneliness and bullying, and if he thought his parents could have prevented it but didn't, that would breed hatred.
He would be overjoyed. It's his parents, after all.
At the start, Harry would be stunned. His whole life has been built on the idea of his parents being heroes. When he realizes they betrayed him, he would be heartbroken. He might go on a journey to find out the real motives behind their actions. Along the way, he could become bitter and vengeful. However, he might also find some inner strength and decide to rise above the betrayal. He could use it as a motivation to break free from the shadows of his parents and create his own path, but not without a great deal of emotional turmoil first.
Often, the Justice League's hatred for Batman in fanfiction is demonstrated by their actions. They might exclude him from important missions or decisions. For instance, they could form a subgroup within the league and intentionally leave Batman out, showing that they don't want him involved. This can also be seen in the way they interact with his ideas. They may quickly dismiss any suggestions he makes without proper consideration just because of their dislike for him. And sometimes, they may even plot against him in the fanfiction, trying to undermine his influence within the Justice League.
In some fanfics, Hermione's abusive parents might be shown as neglectful. They could be constantly criticizing her intelligence or magical abilities. For example, they might not understand her love for books and learning magic, and instead push her towards more'muggle' - appropriate activities. This creates a contrast to her life at Hogwarts where she is celebrated for her brains.
Hermione's parents in fanfiction can be portrayed in various ways. Some fanfiction authors might give them more magical abilities or knowledge than they actually have in the original story. This could be to create more interesting plotlines. For instance, they could have a long - lost relative who was a powerful wizard and this connection is explored in the fanfic, which in turn affects Hermione's journey in the magical world.
It's often shown as a very intense and consuming force. Characters filled with this power might have a dark aura around them in the fanfiction. Their eyes could glow with a menacing look, signifying the 'Power of Hatred' within.
It might make him see them more as real people. Before, they were just an idea of parents, but the trunk could contain things that show their personalities, like their sense of humor or their interests.