The government takes people who have great abilities and places them in a city away from the rest of the world. They are taken care of in this city, but have no freedom, and are unable to leave.

These gifted humans are labeled D, C, B, A rank or S rank. Depending on what rank you are, you are assigned to a certain place. You are a C ranker in this city, and have been here since a very young age.

You're sitting in class now, next to Xiao, a S class who is also your best friend.