In the year 24XX, a world called Shugo is reborn from the ashes and wastelands of Earth. This world is a place in which science cannot possibly comprehend. In Shugo, there exists a life force that every living creature is dependent upon. That life force was never discovered until Shugo's birth, just like the oxygen we breath is never discovered in Shugo.

Human-born Argent Hong Ja Young, vowing to protect her sickly twin sister, is a complex warrior. She seeks a place where no harm can touch her sister and a goal to pursue for herself. While enduring all obstacles that stand in her way, she gradually starts to understand that her life cannot go on without breaking her own limits. 

Glossary:

Argents: Special species who each carry a unique supernatural ability
Daemens: Gruesome creatures ranging from beasts to humanoids that feed on life-forms to survive
Human-born Argent: Argents born from humans gifted with an ability, thus losing their memories before they acquire it
Cruxes: Manifestations of Argents' abilities, familiars summoned by highly-trained Argents
Shugo: After the year 2399, Earth was destined to destruction, and thus Shugo was reborn from the apocalypse, making home to humans and argents alike.