
Shin Megami Tensei: Synchronicity Prologue is a promotional mini-game designed to advertise Shin Megami Tensei: Deep Strange Journey (also known as Strange Journey Redux). This 2D action game with exploration and platforming elements introduces Jack Frost, a character well-known to fans of the Shin Megami Tensei series and other Atlus titles.
Set just before the events of Shin Megami Tensei: Strange Journey, Jack Frost links his consciousness with a human to navigate and battle hordes of demons. He saves the unsynchronized Jack o' Lantern, who had been frozen by Black Frost, the force responsible for annihilating all previous Jacks who tried to attack. Along the way, they encounter a small creature who introduces himself as J-kun. The Jacks journey through the various Sectors of the Schwarzwelt to confront and defeat Black Frost, facing formidable foes like Bifrons, Decarabia, Alice, and Girimehkala along the way. After overcoming the last of these, they reunite with J-kun, who reveals that he once remembered being human—until he activated a synchronicity program sent to him, transferring his mind into a demon's body within the Schwarzwelt. The Jacks come to understand that destroying Black Frost is the only way to restore J-kun to his original form. After defeating Black Frost, J-kun appears and explains that Black Frost is the missing fragment of his own mind. He asks the Jacks to destroy it in order to free him and give him a chance to return to his human body. The Frosts comply, successfully liberating J-kun. The credits roll with a series of world news updates, including the fate of a renowned programmer (depending on the ending), a strange blizzard in Antarctica, and the establishment of the Schwarzwelt Joint Project.