Board Thread:General Discussion/@comment-27601640-20160113032010/@comment-25942629-20160118172715

The circles keep the demons trapped. I believe they restrict the demonic auras so that they cannot lure people in so easily. That part should be the same as the anime. May I ask why you're not allowed to? These circles are actually really complex, so it's highly unlikely anyone would be able to copy them in real life.

Here's an example: