The School Beauty Summoned Me Through the Contract of Cause and Effect

No system, single female protagonist, no brainless villain, fantasy novel about urban immortality 300 years ago, Ao Ming's fiancée Fengli died under the attack of demons from outside the territory. Ao Ming tried his best to defeat the enemy but could not protect his lover. 300 Years later, the two met again, either a compromise of heaven or the beginning of a change in the overall situation.