In the previous era, the City of Sin was named the Guardian City. It was a commonly known nickname given to this city after it helped the humankind defend against the foreign kind.
Legend has it that this city was full of secrets. One of the most famous guesses was that it contains the secret method that teaches people how to fly!
Of course, this was merely a guess and has not been tested. But that alone was enough to make everyone curious.
Sadly, everyone who came to investigate this city has always left the city without any valuable information. As time went on, less and less people visited. Slowly, everyone forgot about the Guardian City.
Now, nobody even remembered that glorious name and was treating it like a landfill that was only good for trash.
One has to admit that this was tragic and sarcastic.
The city that once protected the humankind was not only forgotten by the humankind, even its name turned into one that contained the word "sin".