Cthulhu Gonfalon
In the world, there were gods who obeyed the rules, whether good or evil. But there were also evil gods who defied the rules. When a traverser was confronted by the rules that he could never conform to, the resulting collision marks the beginning of the story of an evil god… This is the story of a good man who transformed into a great jellyfish, then traversed his world to arrive at a world of swords and magic. His journey of searching and exploring eventually led to him remaking nature and changing the world.
The Nargacuga that the man in black was riding was a sub-dragon. Although there was a big difference real giant dragons and sub-dragons, they were still an astounding creature to ride. The hunters rode nothing but ordinary steeds, which weren't even worth mentioning compared to sub-dragons.
Although the so-called sub-dragon was essentially only a beast, it was a beast transformed by giant dragons using their own blood as a catalyst. Thus it had nearly reached the peak capacity of a beast because its blood had been optimized from years of repeated experiments. As long as it had sufficient food and time, every one of them could eventually become a devil monster.