Existence is a bloody story of betrayal and revenge set on a savage world filled with war with the boundaries between worlds weakened. The book's protagonist was left for dead at a young age by demons who murdered his mother during their first invasion, only to have his wife later killed during their second invasion. Stricken by grief and madness, he exhibits a change in personality as he erupts into murderous fits of rage and becomes obsessed with getting revenge on the demons and the ones who orchestrated the event.