[Warning: This is a BL novel, and mature scenes ahead!] Chen Ming, an ordinary twenty-five-year-old office worker, falls into a pit one day right on his face. The next moment he opens his eyes to a little chick flapping its little wings on his face. "Yo, I'm your system, Chick, and I'm a reverse harem system." The chick flapped his wings as if doing a happy dance. "Congratulations user, since you have fallen into the pit, consider yourself lucky because now, you'll be granted a wonderful opportunity to be done by two men!" "Wait, I'm straight," replied Chen Ming straightforwardly as his face remained cold and composed. "So what?" The chick waved his non-existent hair back as he said, "You don't want to be done by two men? I can offer you more if you want." "What if I want to refuse?" "You'll die." "....." The boring life of Chen Ming suddenly changed, especially because he wasn't fucking bent in the first place!
The city of Merfolks was huge, deeper, so deep that no human could reach the city gates even if they swam the deepest. At one point, they would be engulfed by extreme darkness, so much so that they would not want to cross the threshold. Even if some do pass through that area, they would immediately be killed by the gatekeepers standing in the dark.
Yes, there were two gates to enter the city, one was out in the open while the other was standing in the dark, not being able to be seen by any humans. Once they encounter these humans, they won't be left alive anymore.
In short, no one other than regular fishes could enter this place protected dearly by several powerful beings all across the sea.
Ever since being discarded from the surface of the Earth, these people had nowhere to go nd thus, they decided to stay here and find other small fish races beneath the surface to guard them at all times.