……

On this hurried journey through the inferno, Matthew had already encountered many devils with quite distinctive appearances. Yet, no matter how peculiar or unconventional these creatures were, they all exuded a unique aura that perfectly blended with the environment of the inferno.

Matthew called this the "devilish aura."

He speculated that this was due to the evil root shared by all infernal creatures, bestowed upon them by the Blood River.