Sirius Black fic on Wattpad is a fascinating ecosystem. It often revolves around a few central fixations, like exploring his post-Azkaban recovery, which makes sense given how little canon shows of that. A lot lean into romance, of course—either with an original female character or a reader-insert, frequently framed as 'Sirius Black's daughter' or 'Sirius Black's mate.' The werewolf angle with Remus is huge too, obviously, but I've noticed a trend towards more action-oriented plots that pit him against Death Eaters still at large, or even alternate histories where he doesn't go to Azkaban at all.
What really defines the Wattpad vibe, though, is the emotional intensity and the yearning. These stories love putting him through the wringer—flashbacks to his rebellious youth, his guilt over James and Lily, the torture of being locked up while everyone thought he was a traitor. The prose can get very purple, but it works for that platform's audience who crave that deep, cathartic hurt/comfort. You'll also find a surprising number of crossover or modern AUs where he's maybe a rockstar or a CEO; they transplant his chaotic, loyal, damaged energy into new settings, which can be fun if you're in the mood for something less canon-bound.
There's a whole subgenre dedicated to fix-its, naturally. Saving him from the Veil, giving him a happier ending with Harry, redeeming the Black family name—they're wish-fulfillment narratives, but they tap into a real sense of injustice fans feel about his fate. The tone ranges from super angsty to unexpectedly fluffy, with a lot of 'found family' meals in the Grimmauld Place kitchen. I think the platform's algorithm and community features encourage these recurring themes; once a trope like 'Sirius raises Harry' gets popular, you see a wave of similar stories, each putting its own spin on the dynamic.