Summoned to a fantasy world alongside hundreds of others, Takumi is told by a mysterious voice to pick three "Skill Seeds." While everyone else grabs seeds that grant ready-made skills, Takumi notices the crucial difference: a seed is raw material, not a finished ability. This insight awakens him as the world's first "Hacker," letting him freely edit the numerical values of any skill he acquires. He starts by boosting the meager abilities of Mia, a beautiful girl shunned for her non-combat skills, and forms a party with her to humiliate those who looked down on them.

Their journey expands when they encounter Karla, the princess of the Demon Clan, and her guard Gail. Learning that a war between humans and demons has been secretly orchestrated by the Elves, Takumi resolves to stop the conflict. After gathering knowledge in the Dwarf Kingdom about the world's true history, the party heads to the demon capital, Zoff, aiming to reach the Demon Lord himself and dismantle the elven scheme. Along the way, Takumi uses his hacking ability to turn weak allies into powerhouses, rewrite enemy stats mid-battle, and bypass conventional limits of the world's system.

The setting is a typical isekai fantasy realm with RPG-like status screens, skill classifications, and racial tensions. The narrative follows Takumi's rapid rise from confused summon to kingdom-shaking hacker, his loyalty to Mia and later allies, and the larger conspiracy behind the human-demon war. Two main manga adaptations exist: an original series drawn by Tomajirou Hoshi (completed in two volumes) and a reboot titled "Re:" drawn by Uguisu Toki Nana, which continues the story with a fresh start.