We have seen it in many forms, such as rings, skeleton dragons, portals. but what is it?
There has to be a reason for the Bone title, and the bone ring, and the skeleton being. And there are soooooo many theories. But what is it really? Do they ever reveal that in the LN? If so, please write a "Spoiler Alert" so that newbies aren´t spoiled. And if you can help me please do, I need to know.