If Casio's third-stage Deathfang Power could be compared to wood, then, without a doubt, his sixth-stage Deathfang Power was steel, even Fine Steel. This was because it marked the completion of the sixth stage, not just the entry into it. Undoubtedly, this was a gift from a South Dou Red Vulture Fist practitioner who had mastered the Saint Fist level, albeit remotely. No, considering the style of the Red Vulture Fist, this path wasn't one of the Saint Fist but rather the unobstructed path of the Tyrant Fist.
According to Evil Mother's description, in the Deep Space, or rather, a Calamity Source in the World of Calamities, there was a Tyrant Fist elder who practiced the South Dou Red Vulture Fist confronting the ultimate Dark Totem King. They mutually restricted each other's movements, both locked at the source, for thousands of years.
