Man, the Harry Potter fandom really goes wild with time travel and harems, doesn't it? I've stumbled across a few fics where Harry ends up with the Black sisters—Bellatrix, Andromeda, and Narcissa—usually through some convoluted time loop or dimension-hopping shenanigans. One that stuck with me was 'Timeless' by... shoot, I forget the author, but it had Harry getting tossed back to the Marauders' era and slowly entangled with all three sisters. The dynamics were messy but fascinating, especially how Bellatrix's madness was softened by time and Andromeda's rebellious streak got more spotlight.
These stories often play with the idea of 'fixing' the Black family legacy, which adds a cool layer of drama. Narcissa's usually the hardest to write convincingly since she's so tied to Lucius in canon, but when done right, her icy elegance melting for Harry is chef's kiss. Fair warning though—quality varies wildly, and some fics lean way too hard into wish-fulfillment territory. Still, if you dig deep enough on AO3 or FFN, there are gems hidden between the cringe.