The destiny of trainee doctor Kei Nagai changed one day after a fatal accident. Moments after he was killed on the road, Kei suddenly came back to life on the spot, leading to the shocking discovery that he is an Ajin, a race of demi-humans who cannot be killed. Because of that, Kei is pursued throughout the country and eventually captured by the government. He is then held captive at a mysterious research facility, where he is subjected to inhumane experiments. There he encounters another Ajin named Sato, who helps him. Kei soon finds out that Sato is a vengeful terrorist feared amongst both humans and Ajins, and has been plotting to overthrow the government at any cost. Though he is an Ajin, Kei rejects Sato’s extremist ideals and vicious methods, and wishes to be no part of their conflict. However, as Sato begins his shocking bid for power, Kei realises he must join the fight to end his violent campaign. What will be the outcome of a battle between these two demi-humans who can never die? 病気の妹を救うために研修医となった永井圭はある日、事故で死亡。しかし直後、生き返る。絶対に死なない新人類「亜人」と発覚し、崩れ去る圭の人生。国家に追われ続け、非人道的な実験のモルモットとなってしまう。そんな圭の前に突如、人類に牙をむく亜人最凶のテロリスト・佐藤が現れる。自分の運命に葛藤する圭は、佐藤が描く亜人の未来に共感できないでいた。やがて始まる、佐藤による衝撃の国獲りゲーム。衡突する人類と亜人、そして亜人と亜人。絶対に死なない男同士の終わることなき戦いが始まる。亜人たちは、永遠の命をどう生きるのか?