The reason behind it was actually quite simple.
Back when the government fought the Monsters in Hokkaido, it established many military bases in the southern part of the island.
The government had been forced to retreat from Hokkaido in a hurry after losing the war there, and only then had it ended the conflict with the Iron-Cast Palace. There had been no time to destroy or seal off the military bases.
After Machine City was founded, it occupied those bases and acquired the weapons and equipment stored inside.
But the arsenal at the largest military base in Sapporo had been secretly sealed away. Nobody knew what was hidden inside.
It was only after sorting through the documents at the base that Machine City discovered the arsenal in Sapporo contained a powerful secret weapon.
According to the decrypted files, it was a newly developed weapon intended for use on the Hokkaido battlefield. But the government had hastily retreated from Hokkaido just after its development was completed, leaving no time to take it along.
This secret weapon could be used not only against Monsters but also against humans. No carbon-based life-form could escape its attack.
If the Iron-Cast Palace got its hands on the weapon, it could threaten Honshu in turn. So even during their hurried retreat, the government had not forgotten to seal the arsenal.
After decrypting the files, Machine City had been trying to obtain the secret weapon.
But they had no way to open the arsenal. According to the warnings in the files, forcibly breaking into it might directly release the secret weapon inside.
So Machine City had no choice but to keep sending people to Tokyo to search for the key and password that would open the arsenal.
For over a decade, everyone they sent to Tokyo had