A character from Honkai: Star Rail. Leader of the Stellaron Hunters, known as "Destiny's Slave".
Has yet to be confirmed in-game, though a humanoid form has possibly been leaked, and a popular fan theory holds him to be the black cat seen in Kafka's CG (post #5616455), as well as other official arts featuring the Stellaron Hunters (post #7050819, post #7145868, post #9068092).