In the year 2XXX, after repeated global wars, the Earth's environment collapsed, and humanity faced an existential crisis.
People built the ideal city "Agartha" underground as their last hope. There, everyone lived in equality and tranquility.

Meanwhile, those left behind on the surface were forced to live in the "Shelters," which were destined to collapse.

The protagonist, Setsuya, was living a mundane life in the orphanage "Garden of Hope" in Agartha.

However, his peaceful daily routine suddenly changed one day when he awakened to a mysterious power.

In his surprise and confusion, a mysterious black-haired man appeared before Setsuya.

"You are in danger." — Those words greatly shook Setsuya's destiny.

What is the hidden truth behind the ideal city "Agartha"?

Setsuya's chosen path will greatly shake the fate of humanity.
In this chaotic era, what will he choose and what kind of future will he build?