The protagonist, Sasahara Yuuki, finds himself in a world that is not quite his own Earth, where concepts like magic and fantastical creatures are becoming commonplace. His initial confusion about his new reality is amplified when his high school classes begin to resemble game scenarios, with problems involving party compositions and combat strategies. He learns that this world has been connected to another dimension, "Grandia," leading to the influx of a power called "Genryoku" (magic power). This has drastically altered the development of technology and culture, with video games and anime from his original world being scarce or non-existent, replaced by a focus on combat and military applications.
Yuuki's friend, Shousuke, a diligent student, initially dismisses Yuuki's game-like thinking but soon witnesses the strange new reality firsthand. Yuuki discovers that combat training is now a mandatory part of the curriculum, with students exhibiting superhuman abilities. He visits a VR training facility, a place that was once an arcade, and witnesses incredible feats of speed and strength from his classmates. Despite his own developing physical enhancements, Yuuki struggles to keep up, feeling out of his depth.
His journey to understand this new world leads him to explore various training facilities and research institutions, encountering advanced technology and individuals with extraordinary abilities. He learns about the "Otherworld Investigation Team," a group dedicated to exploring dangerous gates that have appeared between dimensions. Yuuki also learns about the powerful "Akiyama Company," which has become a dominant force in this world, involved in everything from weapon development to diplomacy.
Yuuki's path takes a significant turn when he participates in a "Summoning Experiment" in Tokyo, a process that allows individuals to potentially acquire artifacts or powers from Grandia. While many students summon weapons or magical items, Yuuki's summoning results in the manifestation of a sentient soul that refuses to be bound to him, but instead wishes to live alongside him. This soul is revealed to be an ancient elf, a being from a bygone era, whose existence poses a significant historical and political dilemma.
Due to the immense value of this ancient elf, Yuuki's life is irrevocably changed. He is granted a special status, with the Akiyama Company providing him with housing and resources, but also placing him under their supervision. He is enrolled in the prestigious "Schweinritter Comprehensive Training Academy," a top-tier institution that trains individuals for combat and interdimensional affairs. His life becomes a blend of rigorous training, learning about the new world's history and magic, and navigating the complexities of living with an ancient elf who has chosen to coexist with him. The narrative hints at a larger conflict and the protagonist's potential role in the unfolding events of this altered reality.