A prevalent theme is mutual respect. Fanfictions often show how they come to respect each other's skills and abilities. Also, there is the theme of cooperation. They might join forces to face a common enemy or solve a problem. For instance, in some stories, they work together to stop a dark wizard who is causing trouble in both their wizarding communities. In addition, the theme of personal growth can be seen as they influence each other's development as wizards and as individuals.
The friendship between Harry and Viktor in fanfiction might also be influenced by their relationships with others. Viktor may befriend Harry because he sees Harry's loyalty to his friends, like Ron and Hermione. Harry, on the other hand, could be intrigued by Viktor's mysterious nature. They could start by sharing small conversations, perhaps about their families or their dreams, and gradually grow closer as they find more in common.
One common theme is the discovery of their soulmate bond. Usually, they start off not knowing about it and then gradually realize their special connection.
One possible plot could be that they team up for a magical tournament that's different from the Triwizard Tournament. They discover they both have a passion for a rare branch of magic and decide to research it together, facing various challenges along the way.
Overcoming differences is also a big theme. They come from different wizarding cultures, so in many fanfictions, they have to work through those cultural gaps as they become mates. For example, different magical traditions and social norms in their respective countries.
One great fanfiction could be about Viktor Krum visiting Hogwarts again after the Triwizard Tournament. Maybe he comes to teach a special Quidditch training session for the students. In this fanfic, he could interact with Harry Potter and other characters in a new and exciting way, sharing more about his own school, Durmstrang.
Maybe Viktor has been cursed in some way in the fanfiction, and his actions towards Hermione are involuntary. Harry, being observant, picks up on the strange behavior. He may call upon his friends for help, like Ron. Together, they could form a plan. Harry might use his invisibility cloak to get close to Viktor and Hermione without being noticed and then use a powerful stupefy spell to stop Viktor before he can harm Hermione. And then they would figure out how to break the curse on Viktor.
Viktor might be shocked at first. He could feel a strong sense of protectiveness towards Harry. Maybe he immediately tries to comfort Harry and assure him that he's not alone anymore.
Sure. One popular Harry and Viktor fanfiction is 'The Bond Beyond Competitions'. It explores their relationship post - Triwizard Tournament in a really interesting way, showing how they overcome the initial rivalry and become friends. Another great one is 'A Different Kind of Magic' which delves into a more magical connection between them that goes beyond the normal wizarding world relations.