Taking place after the events of Heaven and Earth and before Exodius, Behind the Line depicts the moments of boys and girls after Soushi Minashiro returned home.

Episode 13 included with the Blu-ray/DVD release.

Two hundred years ago, on the Battlefield of the Blue River, the last remaining army of the Empire of Light collapsed in the midst of demonic outcries. As the last Field Marshal and Emperor fell, the chaotic world of the Western River no longer had a common ruler. Factions were formed and endless conflicts ensued, military might became the only currency of survival, and the dream to reunite the lands became the sole goal of many rulers in the generations that came after. In the south-eastern part of the land, a powerful faction with over two hundred years of history – House Zichuan – fought off the Demons to the east, defended against the House Liufeng to the west, and contained the House Lin to the south. In order to accomplish their great ambitions and extend the bloodline of their family, countless heroes of Zichuan gave their lives in order to make this magnificent hymn come to life. This is a story about this legendary family and a hundred years of their blood and tears.

Due to the incredible success of the Sibyl System, Japan has begun exporting the technology to other countries with the hope that it will one day be used all around the world. In order to test its effectiveness in a foreign location, the war-torn state of the South East Asian Union (SEAUn) decides to implement the system, hoping to bring peace and stability to the town of Shambala Float and keep the population in check.

However, a group of anti-Sibyl terrorists arrive in Japan, and the Ministry of Welfare's Public Safety Bureau discovers significant evidence that the invaders are being aided by Shinya Kougami, a former Enforcer who went rogue. Because of their past relationship, Akane Tsunemori is sent to SEAUn to bring him back, but with their last meeting years in the past, their reunion might not go quite as planned.