Takuya Arima, a high school student at Sakaimachi Academy, lives with his stepmother Ayumi following his mother’s death in childhood and the disappearance of his historian father, Koudai, in a rockslide. Inheriting the Reflector—a device enabling travel across parallel worlds—he ventures into alternate realities to unravel his father’s fate and confront existential threats endangering his universe.

Gifted with sharp deductive instincts and a fearless demeanor, Takuya navigates perilous scenarios through curiosity and pragmatism. Despite academic struggles, his resourcefulness surfaces in combat and problem-solving, employing self-taught swordsmanship and tactical wit to overcome adversaries, though outcomes vary. A flirtatious streak leads to bold remarks toward female allies, yet beneath lies fierce loyalty, driving his resolve to protect those he cherishes from personal and universal peril.

Complex relationships anchor his journey: a charged, ambiguous dynamic with Ayumi, blurring familial and romantic boundaries; a past entanglement with Mitsuki, a teacher; and sparring, tsundere-fueled exchanges with classmate Mio. Central to his mission is Kanna, a enigmatic transfer student whose secrets intertwine with collapsing timelines, their bond intensifying as her ties to the crisis emerge.

Across realities, Takuya confronts moral quandaries—choosing between personal desires and multiversal salvation. His quest evolves from a search for his father into a battle against annihilation, marked by pivotal alliances: nurturing a fledgling nogard that matures into a vital ally, and traversing deserts with Yu-No, a cryptic girl linked to the world’s survival.

Once a disillusioned teen, Takuya’s journey forges him into a guardian of fractured timelines, wrestling with loss, identity, and duty. Motives shift from familial longing to cosmic sacrifice, culminating in choices that redefine love and legacy across diverging worlds, where every decision echoes beyond his own reality.