One idea could be that their soulmate marks only become visible to each other under a full moon. Since Remus is a werewolf, this adds an extra layer of mystery and connection. They start to notice the marks during one of Remus' transformations when Sirius is there to support him, and it sets off a whole new dynamic in their relationship.
The soulmate marks could also cause some initial confusion. Remus, being more reserved, might be hesitant to believe in the marks at first. Sirius, on the other hand, might be more eager to explore. As they deal with their different reactions, they start to communicate more and in the process, their relationship deepens. They might share their hopes and fears related to the marks, and through that, they learn more about each other and fall in love.
In some fan fictions, the soulmate mark could be a shared Patronus. When they discover this, it causes a stir in the wizarding world. People start to question what it means for the future of the fight against Voldemort. Harry and Remus have to decide whether to keep it a secret or use it as a symbol of hope. They also have to deal with their growing feelings for each other, which is complicated by the fact that they are in the middle of a war.
In the wizarding community at large, there could be different reactions. Some traditional wizards might not accept a relationship based on a soulmate mark between someone as young as Harry and an older werewolf like Remus. This could lead to them facing discrimination or being ostracized. However, there could also be those who see it as a sign of hope and a new kind of magic. This would then influence how Harry and Remus interact with the wider wizarding world, either having to fight for their relationship or being embraced as a symbol of change.
Well, Luna might have a soulmate mark that is only visible in moonlight. And her soulmate turns out to be someone she least expected, like a commoner in a world full of nobles. Their romance would be filled with secrecy at first as they try to understand their connection through the mark.
One possible story could be that in a world where everyone has a soulmate mark, Luna discovers that her mark is unique. It glows a different color when her soulmate is near. She meets a mysterious stranger and as he gets closer, her mark starts to shine. They start to have feelings for each other as they explore the mystery of their connection.
One interesting plot could be when they first discover their soulmate marks and are in denial because of their rivalry. For example, Harry might initially think it's a mistake or some kind of dark magic trick, while Draco is conflicted between his family's expectations and this newfound connection.
One idea is that a dark wizard targets Remus Lupin and Sirius Black because of their close relationship with Harry Potter. The fanfiction could focus on how they protect themselves and Harry, and how this situation brings out new aspects of their magical abilities and their bond with each other. They might have to seek help from some unexpected allies within the wizarding world to survive.
One common theme is loyalty. Their friendship was always based on loyalty in the original stories, and in fan fictions, this loyalty often translates into a deep and abiding love. For example, Sirius is always loyal to Remus even when others might shun him because of his werewolf condition.
One idea could be that Garra discovers his soulmate has the power to calm his inner turmoil. Another could be a story where his soulmate is from an enemy village, creating a conflict of loyalty. Maybe the soulmate has a special connection to the tailed beasts too.
One great 'Remus and Sirius Soulmark' fan fiction is 'The Mark of Their Bond' which beautifully explores their relationship through the concept of soulmarks. It delves deep into their emotions and how the soulmark affects their connection.