Tohru Kazasumi becomes embroiled in a multi-universe battle when he discovers an alternate version of himself from a parallel world.

A.D. 2115 - the island nation once called Japan is now known as the "17th Far East Imperial City Management District." The citizens were promised a life of peace in exchange for some of the comfort they were used to having. People believed their lives would never change and tomorrow will be the same as today. No one suspected the impending doom which their society was about to face.—Crunchyroll

The story revolves on a group of gunslingers, each from the two universes (Frontier Stratos and the 17th Far East Imperial City Management District) who participate in Operation Stratos, particularly on a group of four childhood friends: Tohru Kazasumi, Kyouka Katagiri, Kyouma Katagiri, and Shizune Rindo, who all must confront their own flaws and differences when they battle their alternate selves from another universe in order to survive.

A.D. 2115-the island nation once called Japan is now known as the "17th Far East Imperial City Management District." The citizens were promised a life of peace in exchange for some of the comfort they were used to having. People believed their lives would never change and tomorrow will be the same as today. No one suspected the impending doom which their society was about to face. "Degradation"-a rare disease which led to the total disintegration of the human body to a mere pile of sand was slowly but surely spreading throughout the world. Tohru Kazasumi, an ordinary student becomes embroiled in a multi universal battle between his world and the parallel world of "Frontier S (Stratos)." This meant that Tohru must fight himself from an alternate world. Their futures collide as their paths cross. Will both worlds ever find peace?—Aniplex USA

A.D. 2115-the island nation once called Japan is now known as the "17th Far East Imperial City Management District." The citizens were promised a life of peace in exchange for some of the comfort they were used to having. People believed their lives would never change and tomorrow will be the same as today. No one suspected the impending doom which their society was about to face. "Degradation"-a rare disease which led to the total disintegration of the human body to a mere pile of sand was slowly but surely spreading throughout the world. Tohru Kazasumi, an ordinary student becomes embroiled in a multi universal battle between his world and the parallel world of "Frontier S (Stratos)." This meant that Tohru must fight himself from an alternate world. Their futures collide as their paths cross.—Anime News Network