Fanfiction about these three can take many forms. For example, there could be time - travel fics where Harry goes back in time and meets Regulus and Sirius when they were younger. This could lead to all sorts of interesting plot twists, like Harry trying to prevent Regulus from joining the Death Eaters in the first place. Or it could be a fic where Sirius survives and he and Harry explore the secrets of the Black family together, including things that Regulus left behind. There are also fics that focus on the emotional bonds between the characters, showing how the different personalities of Regulus, Sirius, and Harry interact and influence each other.
I recommend 'Regulus and Sirius: A Forbidden Bond'. This fanfic beautifully portrays the complex emotions between the two brothers. It shows how their different paths in life affected their bond. There are some really heart - wrenching scenes that make it a must - read for fans of the Blacks.
They could interact with a sense of newfound peace. Sirius might be the first to approach Regulus with open arms, ready to forgive all the past. And Regulus would be a bit more reserved at first but then slowly warm up. They might sit together in a beautiful, otherworldly garden and just talk for hours, catching up on everything that happened since they were last together.
One common theme is their relationship as brothers. Many fics explore the complex dynamic between them, from their early days in the Black family to their diverging paths. For example, some stories focus on how Sirius's rebellious nature clashed with Regulus's initial loyalty to the family.
There's a fanfiction called 'Regulus's Redemption'. In this, it focuses on Regulus's journey after he realizes the true nature of the Death Eaters. It also weaves in Sirius's attempts to save his brother, despite their estrangement. It's a great read as it shows the complex emotions between the two brothers.
Fanfiction.net is a great place to start. It has a large collection of fanfictions, including those about Sirius and Regulus Black in the lemon genre. Just use the search bar and type in their names along with 'lemon' if you're specifically looking for that type of story.
In the afterlife, their relationship could be one of healing. Regulus, having made amends for his past mistakes in a way, could finally have an open and honest conversation with Sirius. They might start to understand each other's motives better. Sirius could see that Regulus was always trying to fight the dark forces in his own way, and Regulus could understand Sirius' need for freedom and justice. They could spend time reminiscing about their childhood, both the good and the bad parts, and form a closer bond than they ever had in life.
Sirius would be shocked at first. He had grieved for his brother, so his return would bring a mix of emotions like anger for being left in the dark and joy at having his brother back. Their relationship would be complex as they'd have to deal with the past. Sirius might also be a bit jealous if Regulus was getting more attention or if he seemed to have a better plan against Voldemort.
Another option is to check out some Harry Potter fan communities on social media platforms like Tumblr or Reddit. People often share and recommend their favorite fanfictions in these communities, and you might discover some hidden gems about Regulus and Sirius Black.