She is the devil that everyone fears, and he is a college student in the 21st world who loves to read online articles. The two were not supposed to meet, but they met because of an accident...
He was originally here to redeem the black heroine, but he didn't know that the heroine was turning black because of him. Is this a cause or effect...
There should be a main and secondary plot. The main plot is redemption, and the secondary plot is the heroine's darkening process.