Tutorial/"Warden of the Flame, Sebu-Nis-Ili-Rabuti-Lu-Tamati"

The last line of defense before the moon's core. It appears that the only thing that affects it is Archaeolune Energy.
You might be able to use Archaeolune Ripples to destroy it.

Destroy all subnodes connected to the core to completely destroy the core in the guardian's central nexus.