Aww, good question! I recommend a novel called "The Demon Lord is My Apprentice" to you. The female protagonist is a top assassin who has transmigrated to an unknown continent. She has a God-Devil Body that has the Heaven and Earth Devouring cultivation method and is also the Demon Lord's disciple. The male and female protagonists are one-on-one. They definitely meet your requirements! I hope you like my recommendation, Mwah ~😗