Is It a Fairy, Not a Demon?

The beginning of the story. The mermaid princess Lingyu and the son of the Emperor of Heaven, Su Chen, are obsessed with each other. However, due to a misunderstanding, she stabbed him to death with a sword. As punishment, Lingyu was imprisoned in the dark deep sea barrier, and was in panic all day long. Although Demon Lord Shiyi calls Lingyu aunt, he has been secretly in love with her since childhood. Suddenly there was no news about Lingyu. He picked up the feathers and fell into the underworld. He never gave up the search. Four thousand years later. An uninvited guest suddenly broke into the deep sea barrier. He looked similar to Su Chen, and he actually wanted to rescue Lingyu from the abyss with his mere mortal body. At the same time, Demon Lord Shiyi learned that there was a sudden movement in the East China Sea in the human world, and there seemed to be traces of spiritual rain. He was ecstatic and rushed there. Immortals, humans, and demons are about to meet. What kind of fateful entanglements will they be involved in?