Ask for the title of a time-travel novel

He only remembered that the female lead had transmigrated. In that book, there was a past life and present life. It seemed that the male lead was a demon king. The entire clan of the male lead was slaughtered by his father, and he was the only one left.
The male protagonist had a brother who was also a demon. He was very powerful and had helped the female protagonist and harmed her.
In the middle of the plot, the female protagonist had once visited the Mermaid Tribe. It seemed that the thing the female protagonist was looking for was in the Mermaid Tribe. She was chased all the way to the Mermaid Tribe by someone who liked her. However, the female protagonist was inextricably linked to the Mermaid Tribe. Because the Mermaid Tribe had undergone a major change a hundred years ago, the Mermaid Tribe's appearance had remained the same as a hundred years ago. They would not age. It seemed that they needed the female protagonist's blood or something to break the curse. The female protagonist accidentally opened the curse later, and the Mermaid Race returned to their original appearance.
There were three lives in this book. The female protagonist was a mermaid in one life. Later, the female protagonist met the mermaid's priest or princess. The priest/princess was the younger sister of the second male lead in her previous life. She was killed by their father and reincarnated into the mermaid race.
The process of saving people was so difficult. It seemed that the female protagonist had to defeat all the more powerful masters of the mermaid race one by one. If she couldn't do it today, she would come back tomorrow. As a result, she became even more powerful.
Then, the man who was chasing after her caught up.[Why is the man chasing after her? It seems that it's because the woman ran away!] They asked the Mermaid Tribe for the female protagonist, but the Mermaid Tribe refused to give it to them. The man fought with them for 300 rounds, and the female protagonist seemed to have participated in it. She was also the one who injured the man, and the female protagonist also suffered internal injuries. Just like that, she recovered her memory of being a mermaid a hundred years ago. In fact, the memory of the mermaid was most likely related to the murder of the entire race of the male protagonist. Only the memories of the previous life were related to the male protagonist!
Later, the female lead became pregnant. She was locked up in the mountain by the male protagonist's brother until the child was born...
That was all she remembered.

Answer 1

The title of this transmigration novel was " Return to the Ming Dynasty as a Prince ".