“Yeah.” Croix closed his book and put it aside. He stood - he always preferred to stand when explaining - and tried to think of where to even begin. He’d start with a slight repeat performance. “Like I said yesterday, reyvateils are connected to the tower. It’s what gives them the ability to use song magic. The energy is a lot to handle, though, and incredibly taxing on the body. Only pure-blooded beta-types can really handle it. Most can’t live for very long, especially not without life extending agents.”