Beast

a fiery beast that was once close in company to one of the five pillars who took down Terrosemon. It regards the newly wandering spirit with malice, having respect enough to stray no further than the boundaries of its own domain, but can and will rain fire down upon Terros should he trespass. It will never forget the chaos that the spirit had once scorched the earth with, and will forever hold hatred in its heart for the loss of its old companion. 

Any mortal may cross the Byrnlands without issue, but to approach the beast with intent is a whole new game. It will not attack outright, but it is a wary creature; having lived for thousands of years, it knows well that humanoids of any sort are unpredictable. Present and proceed with respect, and the beast just may do the same.

There is also a large temple, built directly into the side of a volcano, where the beast keeps watch of the Byrnlands. It is an ancient ground protected with old magic, fiery runes seared into columns that surround the area, allowing only certain creatures and spirits to pass through (old tales claim the beast itself had enchanted the area after once being betrayed by human hand). Some mortals who bear ancient relics of magic specific to the Byrnlands are capable of passing through, but then it is up to the beast if you are worthy of treading on its grounds.
Those who have passed through and into the temple describe there being a golden flame that burns just over an altar, not crackling but singing with voices of the past, as though it were not fire but a collection of souls that writhe together to glow as one. It is a flame that the beast itself protects, also protected by indecipherable runes that float around the altar. 

It is unknown what the golden flame is, but there is a strong standing theory that it may be the life of the beast itself-- entangled, empowered, and protected by the souls of those it once invested trust into.
It was just about a century ago that the singing flame had turned red upon the death of its last companion, the Byrnlands quaking with the beast's grief and fury. It took many years for the flame to return to its golden state, and for the beast itself to calm, before the Byrnlands were once again at its most safest point to cross.