In 12th-century Japan, swordsman Kurou escapes ghastly pursuers into a deep forest with his servant Benkei. Seeking shelter, the two find themselves within the secluded abode of the mysterious and beautiful Kuromitsu. While they are warmly accepted, the men are warned to never enter Kuromitsu's room. However, driven by innate curiosity and perhaps a condemned love, Kurou peeks through the ajar door, only to find Kuromitsu feasting on the blood of fallen men. He soon learns Kuromitsu is an immortal vampire, and dedicates himself to her—even becoming a vampire himself in order to spend eternity with her. But the cryptic organization known as the Red Army has enlisted the help of Benkei, who betrays Kurou and severs his head. Awaking centuries into the future in an apocalyptic modern-day Japan, Kurou sets off to reunite with his lover and exact revenge on the Red Army.

The Labyrinth is an expansive space deep underground where humans live in clusters known as colonies. Over the years, the surface has become a distant memory—even perhaps only a fantasy to those who have never experienced its wonders. Making sure humanity survives the harsh conditions of the underground, a colony's citizens can take on a variety of specialized jobs. These include Workers, who mine precious ore to fuel the colonies, and Markers, who journey into the Labyrinth's surprisingly lush environment to bring back information that eases navigation. However, humanity also faces a threat to its existence—creatures called kaijuu whose sizes range from that of a small child to an enormous building, and are hostile to any human they see. Moreover, kaijuu that are large enough can force their way into the colonies, further increasing their threat level. Memenpu is a nine-year-old college graduate whose inventions have greatly benefitted the Workers in her local colony. Recently, however, she has been dreaming of a place with a neverending ceiling not bound by bedrock. These aspirations fuel her desire to become a Marker and explore the Labyrinth's vast unknown in search of such a fantastical place. Despite her father Gagumber's vehement disagreement, a certain incident with the kaijuu jumpstarts a dangerous yet exciting adventure that will surely alter humanity's course forever.

Though her trip to Okinawa was supposed to be a lovely excursion to the seaside, college student Kaori Sawahara finds that it is anything but when a horrifying menace emerges from the watery depths. A strange mechanism has taken control of the sea creatures, granting them legs and sending them on land to attack anything in their way. Kaori and her friends—the lustful Erika and the reserved Aki—find themselves caught up in this onslaught, made worse by the creatures' rotting stench of death. Surviving the first assault, Kaori tries to contact her fiancé Tadashi in Tokyo. However, the call is cut short in what sounds like another fish attack. Fearing for his safety, Kaori leaves for Tokyo. With Erika and Aki contending with the attacks in Okinawa, Kaori rushes to find Tadashi, unaware that the crisis has only just begun.

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? (Source: Aniplex USA)