I Am an Undercover Agent in the Demon Country 我在妖国当卧底

The male protagonist was selected as a spy by mistake and sent into the demon country to obtain information about the "Demon Mother's Heart".
In order to hide, the male protagonist deliberately approached the demon Bai Ling, and thus had to join a force composed entirely of demons.
As the only human being, the protagonist seems to be both the hunter and the prey.