A lot of these fanfictions tend to explore the idea of redemption or corruption. For instance, Bellatrix might be portrayed as being 'corrupted' by her dark side, and Sirius could be seen as a potential 'redeemer' in some stories. And of course, the sexual tension and chemistry between them is a big part of the lemon aspect, often explored through their encounters. This can be a very complex and often controversial exploration in fanfiction writing.
There are many fanfiction platforms where you might find Sirius Bellatrix stories, like Fanfiction.net or Archive of Our Own. However, I can't specifically recommend a 'lemon' (which usually implies sexual content) fanfiction as it goes against the rules of many platforms. You can search for non - explicit stories with their complex relationship as the focus on these sites.
One popular Sirius and Bellatrix fanfiction is 'The Darkest Alliances'. It delves deep into their complex relationship, exploring how their different allegiances in the wizarding world might lead to some very interesting interactions. However, lemon content often involves adult - themed or sexual situations which may not be suitable for all readers.
When writing Sirius Bellatrix fanfiction without sexual content, first consider their personalities. Sirius is a brave, rebellious character, while Bellatrix is fanatically loyal to Voldemort. Their interactions would be full of tension. Also, think about the setting. The wizarding world of Harry Potter has its own rules and culture, which should be reflected in your story.
There are some out there. However, it's important to note that Sirius and Bellatrix come from different sides in the 'Harry Potter' universe, so these fanfictions often involve complex character developments and reinterpretations. You might have to sift through a lot to find the really well - written ones.
There's also 'Twisted Fates'. This fanfiction plays with the idea of fate and how Sirius Black and Bellatrix Lestrange could have had a different kind of connection. It's a very creative piece that takes liberties with the characters but still stays true to their core traits. The story is full of unexpected twists and turns that keep you hooked from start to finish.
Sirius's friends, like the Marauders, would be extremely shocked. They would probably be very concerned about Sirius as they know his feelings towards Bellatrix as an enemy. They might try to convince him to break away from the situation, thinking it's some sort of dark plot against him. James, in particular, would be very protective and would want to figure out what's really going on.
Another option is Wattpad. Although it has a more diverse range of content, you can still come across some interesting Sirius and Bellatrix love fanfictions. It might take a bit more searching compared to AO3, but it's worth a look.
One possible storyline could be that Bellatrix, despite her dark past, has a change of heart due to some magical influence or a deep - seated love for the Potter family. Sirius, of course, would be a positive influence. They might raise Harry in a more unorthodox way, teaching him both light and dark magic in a balanced way so he can understand the full spectrum. This could lead to Harry being a more powerful and empathetic wizard, able to bridge the gap between different magical factions.
There's a fanfiction that delves into their backstories. It shows how they were both part of the Black family but took such different paths. Sirius, with his more progressive views, and Bellatrix, with her dark and twisted loyalty to Voldemort. The story might have some interesting flashbacks and interactions that are both poignant and full of conflict.