Military otaku Takayama Junya meets an untimely end when he is shot by a real gun during a paintball tournament in the United States. Instead of ceasing to exist, he awakens in a fantasy world reincarnated as a young noble boy named Raul. He soon discovers he has retained his encyclopedic knowledge of firearms and gained a special ability that allows him to summon modern weapons and equipment at will, turning his otaku dreams into a tangible reality.

Raul is eager to enjoy his new life focusing on combat training and field rations, but peace is short-lived. The Bargius Empire, a powerful human nation, invades his homeland and murders his father. In the aftermath of this tragedy, Raul's mother reveals the shocking truth about his heritage: he is not merely a human noble, but a prince of the demons, a race that has long suffered persecution at the hands of humanity.

Forced to flee the empire's hostile takeover, Raul escapes to the Land of Demons, a refuge for his persecuted people. There, he undergoes harsh training to hone his summoning abilities and gain an understanding of the "Demon of Origin" within him. Driven by a vow of revenge and the responsibility to protect his newfound people, Raul decides he is done running. The boy who can summon the firepower of Earth declares war on the empire, preparing to launch a counterattack to reclaim his home with all guns blazing. The series follows Raul as he assembles his comrades and utilizes an arsenal of modern military hardware to wage a one-man war against the powerful human nations that threaten his kind.