It was too much for the Demigods to handle, and the only one who can stop this problem is Iris with her divine powers.
Since her powers are not fully awakened, the adventurers stepped in to help. They believe that if they all work together, it can be solved swiftly. They will continue to believe in Iris and will fight for her. The first place they have visited is the Tartaros in the underground city, also known as the Hell Town.
Shynic the Champion has built Tartaros for centuries, but it was very mismanaged; it ended up being a mess and was filled with monsters. The adventurers show up and asked Shynic for her help, but Shynic denied their request." Adventurers decide to stay in Tartaros to convince her and end up cleaning up the mess in Tartaros.
The adventurers end up finding out why Shynic decided to stop taking care of the city, and found something else...