Man, I totally get why you'd ask about 'Avenging Angel'—it's one of those titles that sounds like it could belong to a whole universe! From what I've dug into, it's actually a standalone novel, but man, does it have the vibe of a series. The author, whoever they are, packed it with so much depth and world-building that it feels like there's more to explore. I remember finishing it and immediately craving a sequel, but nope, just this one glorious book. Still, it's the kind of story that lingers, like a great single-season anime that leaves you wanting more but also respects its own completeness.
That said, I've seen fans online theorizing about spin-offs or expanded lore, which is always fun. Sometimes a standalone just hits so hard that the fandom runs wild with headcanons. If you're into gritty, action-packed stories with a moral gray area, 'Avenging Angel' might scratch that itch even without a series attached. Plus, there's something satisfying about a story that doesn't overstay its welcome.