It's funny, I've seen a few people lately asking about the big reveal in 'Limitless Abyss'. I re-read the webnovel recently, and I think the twist hits differently depending on how you're consuming it. The core twist is that the MC, Kael, isn't actually a failed transmigrator who lucked into a broken system. The 'System' he's been relying on to cheat his way through the cultivation world is, in fact, the lingering consciousness of the original world's Heavenly Dao, which is using him as a vessel to repair itself after a cataclysm. All those 'quests' and 'rewards' were manipulations to guide his growth into a suitable container.
What got me was the foreshadowing on a second read. Those weird system errors weren't bugs; they were moments when the damaged Dao's control slipped. It re-contextualizes his entire journey from a power fantasy into a really dark, cosmic-level possession story. The moment he realizes he's not the user but the tool being sharpened for a purpose he doesn't understand... it gives the whole 'abyss' title a much more personal, horrifying meaning.