Hajime Nagumo, a black-haired, brown-eyed high school student of slender frame, initially embodies gentle selflessness. Mocked by peers for Kaori Shirasaki’s affections, he masks his isolation with casual indifference. Thrust into a foreign realm, he awakens as a Synergist—a class scorned for its frailty. Betrayed mid-dungeon by Daisuke Hiyama, he plummets into darkness, losing an arm to ravenous beasts. Faced with starvation, he consumes monstrous flesh, enduring agonizing mutations: hair bleached white, eyes crimson, skin etched with glowing veins. This transformation grants inhuman strength and latent magical prowess.

Emerging hardened and calculating, Hajime sheds compassion, fixated solely on survival and homecoming. He executes threats without hesitation, former classmates included, yet preserves fleeting tenderness for companions like Yue, the vampire he weds, and Shea Haulia, a rabbit-eared fighter. Bonds deepen with Tio Klarus, a masochistic dragon, and Kaori, whose tenacity chips at his emotional armor.

Harnessing Synergist skills and Earthly ingenuity, he forges mechanical limbs housing concealed weaponry—revolvers, railguns, armored vehicles. Mastery of ancient magics, including reality-warping Concept Magic, fuels his labyrinth conquests to amass artifacts for returning home. His crusade unveils the deity Ehit’s manipulation of Tortus, culminating in the god’s annihilation.

Post-victory, Hajime restores his hair and eyes magically but retains augmented prosthetics. Reunited with his parents, he unveils a family spanning eight wives and adopted daughter Myu, launching a venture capitalizing on his craftsmanship. Though outwardly aloof, he shields allies relentlessly, straddling the line between reclaimed empathy and the merciless resolve born in the abyss.