I'm Actually the Demon Ancestor

Vance Lee wakes in a cultivation world in the body of the Dark Progenitor of the Umbral Sect, with none of the previous occupant's cultivation. He is an ordinary man carrying the name of someone the sects have spent years being afraid of. The Azure Bloom Sect and the other righteous sects pick that moment to march on the Umbral Sect. The elders come to their Progenitor and ask him to come down the mountain and meet the enemy. Refusing would give him away, so he goes out and plays the part, leaning on the reputation his predecessor built and on the fear that comes with it. He also has a system, which is what he falls back on when the acting stops working.