A duplicated Earth called Musashi drifts as a fleet of eight linked ships after humanity's failed attempt to colonize the heavens. Its people re-enact recorded history from a guidebook called the Testament, hoping to recover the knowledge that failure cost them, but the reenactment has stalled at the year 1648 and apocalyptic rumors are spreading. Student Council President Toori Aoi then discovers that P-01s, an automaton built in the image of his late childhood friend Horizon Ariadust, is in fact Horizon herself, reborn into a mechanical body. This manga adapts the opening arc of the original light novel series.