"The Abyss' Entrance"

Fortunately, the dimensional holes could only transport monsters or spread miasma and could not send out the demons. 

This was why the demons couldn't come out at all and could only rely on dimensional holes to spread out miasma. 

The appearance of these gemstones on this island means that there were a lot of demons who came out of the seal's crack or something. 

However, they eventually died because the entrance to the abyss only allowed visitors to come in, but they couldn't go out. 

The blood of various demons who tried to come out became these gemstones. 

The Abyss' entrance was always a mysterious phenomenon, and many experts said that it was the side effect of the seals. 

Or maybe the seal is wearing off despite various leaders from countless races repeatedly strengthening the seal once every decade. 

There were many cases where innocent people fell into the entrance and disappeared, never to come back.