One possible reason could be that he feels misunderstood by his family or friends. Maybe he has some secrets that he's afraid to share, and the fear of being judged makes him run away.
Perhaps he discovers some dark truth about the superhero world he's in. It could be something related to the Justice League or Gotham City that shakes his beliefs so much that he wants to get away from it all. He might need time to process this new information and figure out what he wants to do, so he runs away to have that space.
In some fanfictions, it could be due to personal growth. Tim Drake might have outgrown the role of Robin or the shadow of Batman. He may want to explore his own identity and capabilities independently, away from the Bat - family. He could feel that staying with Batman is holding him back from reaching his full potential as a hero.
Tim Drake walking away in fanfiction could be a way to explore his character in a different light. It could show his independence. He might be walking away to start his own journey, to figure out who he really is outside of the shadow of the Bat - family. In some fanfictions, this could lead to him developing new skills or making new allies. It gives the writer a chance to take the character in a unique direction, away from the more traditional storylines.
She could run away because of a broken heart. Maybe she had a relationship that ended badly, and she needs to get away from the memories. In the process of running away, she could meet new people who help her heal and grow as a person. This type of storyline often explores the more vulnerable side of fem Tsuna.
In some fanfictions, it could be that he has made a big mistake. For example, if his actions as Spider - Man led to the harm of an innocent person. He would be so guilt - ridden that he decides to run away from everything, including his friends and family in Queens.
Maybe Pikachu is feeling neglected by its trainer. If the trainer has been paying more attention to other Pokemon or is too busy with something else, Pikachu might decide to run away to get some attention.
It could be due to a personal betrayal. For example, if he discovers that another member of the Bat Family has been hiding something important from him that makes him feel he can't trust them anymore. This would make him want to leave and create his own identity away from the family. In fanfiction, this kind of emotional turmoil can drive the story forward.
One reason could be that she has big dreams that can't be fulfilled where she is. Another might be that she's running from a person who's threatening her. Maybe she just wants to explore the world and find herself.
Maybe they run away because they are tired of the constant danger at Hogwarts. They've faced so many threats, and they just want a break. So they run to a peaceful place where no one knows them.
One possible reason could be a conflict of values. Hermione is a strong advocate for justice and equality among wizards and non - wizards alike. Draco, on the other hand, was brought up in a family with pure - blood supremacist views. Hermione might run away from Draco in a fanfiction if she realizes that his views are unchangeable and they are fundamentally opposed to her own. For example, if Draco makes a derogatory comment about Muggle - borns in front of her, it could be the last straw and she decides to run away.
Maybe he wants to escape the constant danger in the UK wizarding world. Voldemort's followers might still be a threat even after his defeat, and France could seem like a safe haven.