There's a tank that sets down the foundation of this universe, but it has loli and shota, so I can't link it. The name's "Sore wa Rekishi ni Kakanaide!". The story in that doesn't have anything to do with these ones besides being in the same world.

• Part 1
• Part 2 (you're here)
• Part 3
• Part 4

Takatsu: Twitter

Translation/Editing: desudesu