Satake Hirofumi is a prisoner on death row for murdering his fiancée. He's also an "Undeadman" who has survived many desperate situations. For this, he has earned the interest of a research institution called "Human Crazy University," which studies real-life miraculous phenomena and the people who become entangled in them. Now a subject of their research, Satake relates to them his memories of his immortal, yet unhappy, life. Why did he kill his fiancée? Soon enough, the truth sheds light on a much bigger conspiracy...

It is the dark century and the people are suffering under the rule of the devil, Vandel, who is able to manipulate monsters. The Vandel Busters are a group of people who hunt these devils, and among them, the Zenon Squad is known to be the strongest busters on the continent. A young boy, Beet, dreams of joining the Zenon Squad. However, one day, as a result of Beet's fault, the Zenon squad was defeated by the devil, Beltose. The five dying busters sacrificed their life power into their five weapons, Saiga. After giving their weapons to Beet, they passed away. Years have passed since then and the young Vandel Buster, Beet, begins his adventure to carry out the Zenon Squad's will to put an end to the dark century.

Transferring the human consciousness into a robotic "I-Machine" is now a reality thanks to the discovery of a valuable ore called "orichalt." However, there is the possibility of the consciousness failing to return to the host's body, rendering them stuck inside their new metallic frame for good. Such is the situation of members of the Excavate Company, a reckless band of I-Machine miners led by the notorious Grayman that aims to gather orichalt for profit. During a mining incursion, the group rescues Maya Mikuri, a student who was abandoned by her crew. Accused of stealing classified information on orichalt by her former colleagues, she joins the Excavate Company in hopes of clearing her name. They then begin an adventure that will change their lives—including that of Ido, an ace member of the group with no memory of his past. For the first time, Ido might have the chance to rediscover his true identity. [Written by MAL Rewrite]

It mainly tells the story of Gu Fei, a super warrior but a physical education teacher in school. He started playing online games on the recommendation of his students, but he mistakenly chose the profession of mage, and finally became a melee violent mage, embarking on a new game path.