"Visage", Rich McCormick
Black Library, Horus Heresy series.
Of course fuck Erebus, but it's a nice story giving the character a bit of depth.
It shows and made me realize what's so unsettling in Erebus as a character: he's an ideal mid-high-level corporate leader, who gets shit done to advance organisation's goals with ruthless efficiency, with absolute disregard for other people and outside costs, while staying in line and not challenging higher leadership, even accepting the worst chastising by higher-ups. Every corporate C-level and VP dreams of such directors. Erebus is peak late capitalism. So, fuck him.