All Carin wants is to be a normal girl, or as normal as she could be when her family was hiding out from her evil maniac of a father. Alone hunting in the woods one day, she is captured and turned into a mutant child and plunged into a world of hideous cruelty and pain. Carin's father has become one of the people that create monsters out of children, so they can fight in arenas like gladiators in medieval times. Her wish changes from being a normal girl to getting back to her family before she is killed in the fights. The only problem is, can she do it? The level of power and skill she is going up against is more than anything she's ever experienced before, and her competitors will have no qualms about killing her.

"The Umbra Monstrum have entered this dimension. Gather the warriors. We must protect the humans at all costs." Deep in the Apennine Mountains, hidden from human eyes lives the Apennine tribe. Once great warriors who used to roam the world, they were forced to come together and go into hiding, becoming no more than a masked society, who still dedicate their lives to protecting the rest of the world.