One seemingly normal morning, Regulus had woken up to find Sirius’ room looted of its stuff – only a few pictures and horrid posters left up on the walls. His trunk was gone, as was all of the detritus that typically littered his older brother’s floor.
Regulus had wanted to pretend that he was shocked by this turn of events. But, really, Sirius had been warming up to leaving ever since he came back after his first year at Hogwarts. What he really found surprising was that Sirius hadn’t even said goodbye. Hadn’t even hinted that he was planning to leave.
And as he watched the seven years of student begin streaming in, Regulus drifted off. Knees tucked up close to his chest and forehead stuck to the cool window, creating little puffs of fog with his slowing breath.
As Regulus finally lost consciousness, he could just feel the hair on the back of his neck raising in warning... of something...he thought. Perhaps.
Regulus returns to Hogwarts after a seemingly normal summer. Except Sirius ran away, and he's not really sure why. He's just haunted by a shadow in the corner of his eye and gaps in his memory.
Warning: graphic depictions of violence
https://archiveofourown.org/works/38473963/chapters/96157111
He is a Slytherin, a Black, and an ex-Death Eater. Of course he makes it out of the cave.
Regulus sets out to destroy the Dark Lord's Horcrux with no one but a house-elf to help, until he realises his task is bigger than he alone can handle. Reluctantly he turns to the only man Voldemort fears for assistance - Dumbledore - who loans out his pet wolf for the job, much to Regulus's dismay. Together they embark on a hunt for Horcruxes - a long and arduous journey that both makes friendships and destroys them. And a few people get hurt along the way.
Slowburn Wolfstar, Regulus character development, a very flirty (but platonic) Regulus and Remus friendship, and a canonically manipulative Dumbledore.
https://archiveofourown.org/works/35626792/chapters/88824535