Hato no Senki tells the story of a young man named Hato Yokoyama that plays a game called DDS-NET in which players can fight against demons. He encounters a Pixie being attacked by other demons and protects her. When the game prompts him to kill her to receive an item, he refuses and discovers a strange symbol has appeared on his hand. This symbol teleports him to an area where he meets a young girl that Hato assumes to be an NPC. Cu Chulainn appears addressing the girl as princess and assumes Hato is another demon. His demeanor changes when he discovers the icon on Hato's hand and explains that Hato is the Messiah. He asks Hato to become his ally in protecting the princess.