This was a really great and very detailed article about Tower of Elements in the Lexington Herald Leader:
So came the tale of how you must defend your tower from the onslaught of The Void army, a group that rose to prominence in Primordiax.
“Basically, The Void abhor existence,” Hartman said. “They are a power of nihilism, and they want the universe to cease to exist.”
So as The Void approach your tower, you must defend it by matching the runes inside. Each match sends out a powerful blast that can destroy enemies in its path.