herrscher_of_the_end
Kiana's Herrscher form in Benghuai Xueyuan, God Kiana, the Herrscher of the End. In the Retrospective Era, she manifested as a result of Kiana fusing with Sirin, the Herrscher of the Void.
The design is also used for the Final Herrscher in the Previous Era of Honkai Impact 3rd.