In the mid-21st century, high school student Akira Himegami and his foster sister, the brilliant AI researcher Towasa Omagi, confess their love and promise to marry. Their future is cut short when an anti-AI extremist shoots them both at a public conference. Akira is critically wounded and placed into cryogenic suspension to save his life, leaving Towasa behind in a world on the brink of disaster.

Akira awakens 200 years later in the year 2238 to a world he no longer recognizes. Society has collapsed following a devastating war between humanity and rogue AI, an event that reduced the global population from billions to roughly two hundred million. The ruins of civilization are now governed by a monolithic organization known as OWEL, which strictly controls pre-apocalyptic technology and has replaced traditional marriage with a new system called Elsie. As Akira struggles to comprehend this harsh new reality, he is rescued by an android named Yuugure, who bears an uncanny resemblance to his lost love Towasa. She immediately makes a startling proposal: "Akira, please marry me".

Believing that the real Towasa might still be alive somewhere in this changed world, Akira agrees to journey with Yuugure. As they travel through the post-apocalyptic landscape, they are joined by a young girl named Amoru, who dreams of becoming a picture book author after losing her parents. The group faces repeated confrontations with OWEL forces, who view Akira as a valuable relic from the lost age of technology. They also encounter other models from the "Outside Series," a line of weaponized androids originally created by Towasa to end the AI war, including the formidable combat android Yoiyami, who shares Yuugure's design.

Throughout their journey, a deeper truth about Akira’s existence is revealed. He is not the original Akira Himegami, but an android duplicate created by the original, who survived the assassination attempt and lived for decades. The real Akira, now an elderly man, constructed this copy to carry on his search for Towasa after his own body began to fail, but never activated it. Learning that his memories and identity are artificial shakes Akira, but Yuugure confesses she withheld this knowledge so he could experience life as an individual rather than a mere copy. Ultimately, the group finds the elderly, original Akira, who has been using the android network to observe his duplicate's journey. Yuugure delivers a final message from Towasa, who has long since passed away from natural causes, allowing the original Akira to die in peace. In the end, the android Akira accepts his own identity and finds genuine love with Yuugure, with whom he chooses to build a future.