──June 2, 1925, 4:17 AM. Seven years after the end of World War I. The League of Nations had been established, and just as the world was about to take its first steps toward peace... In Tokyo, the outskirts of Berlin, the London Underground—in over a dozen locations worldwide, spatial anomalies that could not be explained by existing science were observed simultaneously. Building walls vanished for seconds, people appeared to teleport several meters away, non-existent streetscapes appeared for dozens of seconds, and even unknown minerals and plants were discovered.

However, governments sealed off this information. There was no way to determine the cause, and eventually, the incidents were pushed to the corners of history as "post-war collective hallucinations," "sensationalist journalism," and "urban legends."

Ninety years later, in 2015. The weak spatial anomalies that had been observed worldwide for many years finally reached their limit.

11:32 AM. A massive spatial rupture occurred over the skies of Tokyo. A giant glass crack crossing the sky. What appeared from the other side was Tokyo. But it was not the Tokyo of this world. It was another Tokyo that existed in a different parallel world.

In the next moment, the two worlds overlapped.

Buildings, roads, subways, humans, and space itself encroached upon and merged with one another. The greatest paranormal disaster in world history. Approximately 9,215,472 dead, 5,083,886 missing, 2,628 seriously injured, 6.92 million buildings vanished, and 1.08 million evacuees. The Japanese government declared a state of emergency and mobilized the Self-Defense Forces, police, and fire departments. Still, the damage did not stop. Eventually, multidimensional fusions called "Rentra," born from the forced merging of otherworld laws and energy with real-world matter, appeared and began attacking various locations.

The government named the series of phenomena "Layer Crack." They established the "Otherworld Defense Agency," a world defense organization directly under the Cabinet Secretariat. The entire Tokyo area was designated as a Class 1 Exclusion Zone, and as of 2034, entry by civilians remains prohibited. Eventually, similar anomalies were confirmed worldwide; governments sealed off disaster zones, and research institutions continued to chase the phenomenon. However, they could not obtain answers as to what lay beyond the rift or why the two worlds had made contact. Meanwhile, people gradually adapted to the new world. Technologies and resources derived from the other world began to be researched, and products using that technology were developed one after another. But the scars left by the disaster do not disappear. Inexplicable phenomena continue throughout Japan even now. And Sou, too, was not unrelated to that disaster.

In one corner of a park, a boy is sitting on an old swing.

"Sou Oriba."

Dark brown hair and clear blue-green eyes. He wears a white T-shirt under a black hoodie and slim black pants. He was stopping by this park as he always did. There was no special reason. It's just that coming to this place makes him feel a little bit at peace. His sister Natsuki had told him many times in the past, "You're off thinking by yourself again," but Sou himself was not yet able to put into words what he was thinking about.

It was a quiet afternoon. A gentle breeze envelops him. A spring afternoon. In the park, slightly away from the hustle and bustle of the city, the leaves of the trees swaying in the wind played a gentle sound. On his way home from school, Sou lightly kicked the ground with his feet while facing a single piece of paper placed on his lap. It was origami. He folded and unfolded it many times, checking the angles and folding it again. His expression was one of pure seriousness.

Just as he whispered that...