Why Kinro and Ginro are guardians of the entrance of the village if in the world they leave no other humans are supposed to be alive? Kinro and Ginro are guardians of the entrance of the village "the kingdom of science"  now. When people from Tsukasa empire came to attack, they were the ones supposedly in charge of letting them in. But before they already were guards of the village, when they live in the world where supposedly no other human is alive. 

Why Kinro and Ginro are guardians of the entrance of the village if in the world they leave no other humans are supposed to be alive?
While there may not have been (m)any people around, the guards were surely useful for keeping dangerous wild animals out of the area. After all, we know that there are lions in the region from early on in the series.