Away from home for 10 years, Azuma Kazuki had no idea what was awaiting him upon his return. He certainly did not expect to be attacked by dozens of heavily armed people and taken as their prisoner. Fortunately, Azuma's stay in captivity is short. Wielding a strange sentient weapon—known as Bubuki—upon her right arm, his childhood friend, Kogane Asabuki, rescues him. After escaping, Azuma learns that he too has the power to control Bubuki. Together with his new companions, he must revive the Buranki titan named Oubu, that sleeps somewhere deep underground. With this knowledge and purpose, a new path to unearth the truths behind the Buranki opens before Azuma.

In the year 2020, a nation faces the pervasive threat of the Others—mysterious monsters who fall from the sky and feed on human brains. At the same time, psionics, a hormone that gives certain people extrasensory abilities that are effective against the Others, is discovered in the human body. Subsequently, the nation's founder establishes the Other Suppression Force (OSF) to combat these monsters and save humanity. Commonly referred to as the Scarlet Guardians, young individuals with psionics undergo intensive training to join this group. One day, the nation prepares an induction ceremony for the exceptional recruits who completed the grueling training to become Scarlet Guardians. Among these young elites is Yuito Sumeragi, the determined son of the nation's founder; at the age of five, he was rescued by a woman in the OSF. To repay this debt, he joins the organization, eager to put his training to good use. As he meets his new comrades, he faces a big problem—the woman who saved him years ago closely resembles one of his teammates. However, this should be the least of his worries—unbeknownst to him, a conspiracy is brewing, one with the capability to shake the entire country.

Konoha Akisato's love for bishoujo games—a type of entertainment focused on interactions with beautiful girls—has always nurtured her aspiration of becoming a popular artist. However, as Konoha secures her first job as a sub-illustrator at the game company Blue Bell, she confronts the harsh reality surrounding her favorite genre. In 2023, the bishoujo game industry is overrun with cheap, repetitive, and low-effort releases, with Blue Bell at the core of the problem. After stumbling upon a vintage game store and reminiscing about the impressive titles of the past, Konoha suddenly winds up in the year 1992—just as the bishoujo game industry was beginning to flourish. Konoha struggles to accept her new circumstances until she joins Alcohol Soft, a small game company willing to employ her as an illustrator. Although she believes her skills from the future will propel her to success, technology and illustration are considerably old-school, and she must promptly adapt if she wishes to fulfill her dreams.

Ryouhei Arisu is a high school student with no ambitions and just wants to escape from what he feels is a meaningless reality. One night when he is with his two friends Daikichi Karube and Chouta Segawa, they see an abnormally large firework shoot into the sky, an event which signals a permanent change in their lives. Blinded by the incredibly bright explosion, the three find themselves transported to what is known as the Borderland. The only inhabitants of this world are participants of a deadly game where specific tasks must be accomplished if they wish to survive. As the three begin playing to determine how they can get back home, Ryouhei finds himself feeling alive for the very first time in his life.