Wuxia: The Impostor Empress Dowager

Gu Tianchen is an elder of the Sun Moon Divine Cult. His disguise technique is incredibly sophisticated, allowing him to change from a man to a woman, or from old to young.

Dongfang Bubai sends him into the imperial palace disguised as the Empress Dowager.

Gu Tianchen's first move is to rule from behind the curtain, gradually stripping the emperor of his authority until he becomes the most powerful person in the land.

A few years later, someone suggests he become emperor and rule as an empress like Wu Zetian.

Gu Tianchen is completely dumbfounded.