Honestly, I've been seeing a lot of buzz about the 'Rise of the Demon God' series lately, especially in some web novel circles I lurk in. My understanding, having dabbled in the first couple books and reading tons of wiki rabbit holes, is that it's a sprawling cultivation/progression saga with a huge cast. But if we're talking key, the absolute core is a dual protagonist setup.
At the heart of it is the titular Demon God, who begins as a young man named Kaelan (or something similar, names sometimes get localized differently). His journey from a scorned outcast with a crippled dantian to an entity feared by heavens is the main throughline. He's ruthless, pragmatic, and his moral compass is... well, it's more of a suggestion. The other pillar is Li Xue, his childhood friend/rival/fated entanglement. She starts on the 'orthodox' righteous path, representing everything Kaelan supposedly stands against. Their clashing ideologies and the slow, painful fracturing of their bond as Kaelan descends is what gives the series its emotional weight.
Beyond them, you've got the Master of the Abyss, a mysterious ancient entity who becomes Kaelan's mentor and the source of his forbidden techniques. Then there's the Heavenly Sword Sovereign, the embodiment of the righteous faction's power and Li Xue's eventual master, who serves as the primary antagonist force for a good chunk of the mid-series. Oh, and the Alchemist Zhu, a minor but fan-favorite character who provides rare moments of levity and crucial resources, proving not everyone in Kaelan's orbit is a world-shaking powerhouse. The cast expands massively with each new realm he conquers, but these are the names you'll see in every synopsis.