the tank has leg?...

-The series plainly takes place in the distant future. Technology had advanced quite a bit, but with the onset of the incredibly long and destructive war, nearly everything was lost. What few relics have survived (Such as the spider tank) are largely remnants of a lost culture. Also, in the lake in which Kanata saw the skeleton that is believed to be that of the "demon", modern guard rails can be seen half-buried under rubble along the rocks underwater.

-Cultures have mixed a lot. The story is set in Seize, a town that is based on an existing one in Spain; French seems to be used a lot (note Noel's name - it's a clearly French name, but it is written in Kanji); the old writing in the ruined school is in Japanese, but neither Kanata nor Kureha knows how to read it.

- It appears that music is used for practical purposes rather than for enjoyment, and it is not formally instructed outside of the army. Kureha is shocked when Kanata suggests that music may have been taught outside of the military. This would also explain why Kanata enlisted as a trumpeter despite having no knowledge of how to play; normally, one would learn to use the instrument before joining the military, but it would make sense if joining the military is the only way to learn.

- Kureha's lecture to Kanata is deceptively significant. She mentions that five soldiers is the absolute minimum number to a platoon. Kanata makes the fifth soldier in Seize, raising the question of just what happened to the former fifth member.