Blood-C is one of those shows that has a dream-like quality to how the plot escalates. The theme and feel shift as the plot progresses. It is not intended to be logical. Instead, it's moment-to-moment action is designed to evoke strong emotions.

(Another similar example I can think of are "Darling in the Franxx" or "Danganronpa".)

To put it simplier, it's a "trippy" show, about a girl swordmaster, who is chopping increasingly more bizzare monsters.