They might start off as enemies. Sirius doesn't get along with his family, so he may not want the Marauders to have anything to do with Regulus. But sometimes, they could end up working together for a common good.
Sirius would probably be angry at first in the fanfiction. He left his family and Regulus was still part of it. But as the story progresses, he might start to feel some regret or longing for his brother. James would be supportive of Sirius' emotions, and Remus would be the voice of reason, analyzing Regulus' actions and motives.
There are fanfictions where they meet in a dangerous situation. For example, in a Forbidden Forest encounter. The Marauders are exploring, and Regulus has gotten lost. They initially suspect each other of ill intentions but then realize they need to work together to get out. And there's also the type where they meet at a pure - blood event, which challenges their different beliefs about blood purity and friendship.
Another good one is 'The Marauders' by an anonymous author. It focuses a lot on their pranks and adventures. It has a great sense of humor that really captures the spirit of the Marauders. You'll find yourself laughing out loud at their antics and also feeling the bond between the friends.
One great 'oc marauders era fanfiction' is 'The Marauders' Daughter'. It has a really engaging plot where the main OC is the daughter of one of the Marauders. The story does a wonderful job of weaving in the original Marauders' story while also giving the OC a unique and interesting backstory.
Archive of Our Own (AO3) is a great platform for 'Marauders meet Regulus' fanfiction. It has a large collection with various interpretations of their meetings. Fanfiction.net is also a well - known platform where you can find such stories. There are different tags and filters to help you find exactly what you're looking for.
They are likely to be horrified. James, for example, would probably be extremely angry that his friend had to endure such a thing. He might immediately vow to protect Sirius from any further harm. Remus, being more empathetic, would be there to comfort Sirius and offer his support in a more quiet and understanding way. Peter, though not as strong - willed as the others, would still be shocked and follow the lead of James and Remus in trying to make Sirius feel better.
Well, Harry Potter is the main character who travels back in time to the Marauders era. James Potter is a significant character as Harry's father. Sirius Black, with his charm and wild nature, is an important part of the story. Remus Lupin, the intelligent and kind werewolf, is another mainstay. Peter Pettigrew, though not always a likable character, is also part of the main cast. And there could be other characters like Severus Snape in some fanfics, as his relationship with Lily and the Marauders was complex and could be explored in the context of Harry being in that era.
Friendship is a very common theme. The OC often forms strong bonds with the Marauders, like they go through adventures together and support each other. Another common theme is the struggle against the dark forces that were starting to rise during that era.
One popular 'marauders era fanfic' is 'All the Young Dudes'. It offers a detailed and engaging look into the lives of the Marauders during their Hogwarts days. It has great character development and a really interesting plot.