First Lieutenant Haru "Arc" Shinozaki is a ghost of the modern world—a lethal special forces sniper haunted by the traumas of war. His life is turned upside down when a military transport carrying apocalyptic WMDs vanishes through a wormhole into Aethel, a parallel world of swords, sorcery, and prophecy.

Deployed with the elite multinational G.A.I.A. squad, Haru's mission is clear: locate the lost aircraft, secure the weapons, and leave no trace. But in Aethel, their arrival is not a secret operation—it's the fulfillment of a prophecy. They are hailed as the "Knights in Green," fated saviors in a land on the brink of chaos.

Armed with 21st-century firepower against medieval armies and mythical beasts, Haru must now fight a two-front war: one for his mission, and another against the ghosts of his past. He must decide whether he is a soldier following orders or the hero this new world desperately needs, all before the doomsday cargo falls into the wrong hands.