The earth of the distant future is covered in thick clouds, and the sun no longer shines. Plants wither, and oxygen is thin. To fight extinction, humankind has developed a technology that turns humans into plants, providing a small amount of oxygen. Is this process sustainable? Is it ethical? Toshiro Kamiya must consider these questions as he's faced with a difficult choice--save his family or save himself.

As Hourai recovers from Ivy's brutal attack, Toshiro investigates the vicious spiriflor's origins. He's led to a place called Paupertown. What will he find in the town's dark and miserable depths?