The book, The Demon of the Evil Crimson Bead, may fit the information you provided. In order to escape from her enemies, the female protagonist hid the God Orb fragment in the male protagonist's body. Although the female protagonist planned to kill the male protagonist and destroy them together, the male protagonist fell in love with the female protagonist and chose the female protagonist in the end, leaving behind a glimmer of hope. I hope you like my recommendation.