Setsu no Hi

Another world is discovered. Creatures there look a lot like primitive human barbarians, so discoverer names it "Inferior". The only link between the worlds is a 5mm hole, so government establishes trade and keeps its existence in secret. But "Inferior" starts to pierce reality of human world, and monsters start to show up. A group of young people with special powers stand up to oppose this threat.

[From vndbreview]