Ichirou Suzuki, a programmer nearing his thirties, is drowning in work. Worn out, he eventually has a chance to catch up on sleep, only to wake up and discover himself in a fantasy RPG world, which is mashed together from the games he was debugging in reality. In this new place, he realizes that not only has his appearance changed to a younger version of himself, but his name has also changed to Satou, a nickname he used while running beta tests on games. However, before Satou can fully grasp his situation, an army of lizardmen launch an assault on him. Forced to cast a powerful spell in retaliation, Satou wipes them out completely and his level is boosted to 310, effectively maximizing his stats. Now, as a high-leveled adventurer armed with a plethora of skills and no way to return to reality, Satou sets out to explore this magical new world.

On the brink of extinction, mankind has downsized and now solely resides in the city-state of Flandore, living in cities encased by glass domes. Beyond the domes exist vicious lycanthropes who thrive in the darkness; among the citizens inside, a clear distinction between the nobility and commoners is in place. The blood of nobles enables them to utilize mana, granting them abilities that exceed human limits and greatly assist them in defeating lycanthropes. Already 13 years of age, noble Melida Angel has yet to manifest her mana, and attends an elite academy where she is mistreated for her lack thereof. In order to help her, Kufa Vampir is ordered by the Angel family to become Melida's tutor. While Kufa seems to be a mere mentor, an ulterior motive lurks behind his job—he is to assassinate her if he confirms that she does not possess mana. Kufa's investigation eventually leads him to determine he must eliminate Melida. However, Kufa is struck by her unwavering determination, spirit, and belief in herself when he witnesses her in a fight, choosing instead to offer a way she can manifest her magic. As Melida learns to use mana with the help of Kufa's teachings, Kufa forsakes his mission and jeopardizes everything to keep his discovery of Melida unknown to the Angel family and his own guild. However, both Kufa and Melida will soon realize that hiding their secret will not be the only challenge they face, as unforeseen trouble is waiting just around the corner.

After unknowingly participating in a kidnapping, college student Yuuya Nomoto finds his friends brutally murdered by Hitomi Uzaki, the high school girl they attempted to abduct. Forced to drive her to an undisclosed location, he finds himself being wagered as the prize for a death match between two Therianthropes, superpowered human-animal hybrids created through advanced gene therapy. As one of these hybrids, Hitomi uses the speed and fearlessness she gained from her ratel genes to viciously dispatch her foe and save Yuuya from certain death. Waking up hours later hoping the whole event was only a nightmare, Yuuya realizes that he has become embroiled in a secret proxy war between four large Japanese business conglomerates, with the winner taking control of the economy. As her sole albeit unwilling investor, his life is now directly linked to Hitomi's ability to participate in underground bloodsport matches known only as Killing Bites.

In the technologically and magically advanced Wahrheit Empire, rumors of a returning catastrophe known only as the "light" causes a disturbance amongst the people. Meanwhile, in the capital of the Empire, transporter Innumael Grauer prepares his daily deliveries, struggling to make ends meet for himself and his sister. Leocadio Wöhler, a newly recruited soldier, assists Innumael whilst commuting to work—unknowingly loading a mysterious package containing contraband artillery belonging to a criminal organization. Innumael is accused of smuggling the package, facing possible execution due to the Empire's strict oversight of weapons in response to the rising disorder. However, unbeknownst to him, the very syndicate that placed him in this unfortunate predicament may save him from this fate, at least temporarily. Elsewhere, Leocadio is assigned his first mission—to apprehend the criminal group known as "Headkeeper," suspected of transporting illegal weaponry. Magatsu Wahrheit: Zuerst follows these two young men on a journey encompassing the Wahrheit Empire, triggering a chain of events that will not only change their lives but also alter the course of the Empire as they know it.