A strange disease is linked to a mysterious hole that leads to an underground world: the Asylum. "Sleepers" come to this world to fight strange monsters and retrieve unknown resources. Now, a young man who dreams of being a hero has arrived at the Asylum.

As Shigure begins to settle into his new life as a Sleeper, he begins to wonder what he is good at and what he can accomplish at the Asylum.

Larry goes on a dangerous and illegal mission deep in the Asylum and forces Shigure to go with him.

Shigure delves into XO Leslie's past when a mysterious assailant suddenly ambushes him.

Shigure is always embarrassed around Kobato and the rest of the team thinks he might have a crush on her. They hatch a plan to bring them together, but...

The day of the plan has arrived and the team heads towards the Asylum. But when Hayden shows up during the mission, things go terribly wrong.

With Leslie's death, the team is forced to find its way alone. And Shigure starts to have doubts about his mission...

With strong pressure from the command hierarchy, Vera decides to lead a mission to the Asylum on her own.

Vera drives Shigure away from the platoon, but he's not ready to leave the Asylum... yet.

Now trapped in a time loop, Shigure struggles to unravel the mystery behind EL-Cee and Iceman's plans.

Shigure travels through time once more to save Vera and stop Iceman from destroying the world.