Lan Wu is a mermaid demon princess who runs away from home to escape an arranged marriage. While fleeing, she is spotted by a cultivator who tries to kill her. In desperation, she swallows a pill that conceals her demonic aura, but as a side effect, it also sealed her demonic powers.

Ji Lingyue, an aspiring cultivator, happens to be passing through the mountains when she finds Lan Wu listlessly resting beneath a tree. After saving her, Lan Wu decides to accompany Ji Lingyue, and the two of them head to Haochen Mountain to become disciples.