Ping Mo Ce: The Red Sword of Eternal Love.

Five years ago a Western virus swept the Central Plains, transforming people into bloodthirsty monsters. They were called "blood demon." Everyone knows that Ouyang Chun used his ancestral divine sword to kill the source of the virus, the "Demon Ancestor", but unbeknownst to him, his lover, Yue Qingyin's sister Peiru, became infected and a powerful new "Demon Ancestor". Ouyang Chun confessed that he had indeed killed many undeserving people to keep Peiru alive, but he had found a way to transform Peiru back into an adult and would turn himself in as soon as he had done so.