User blog comment:Themasterofantics/Monster Girl Theory/@comment-2405:9800:BA13:9270:C2C:31B5:D699:C9D2-20191015175706

The Echidna part is mostly inspired by Greek mythology. According to it, Echidna is the wife of Typhon, and generated many offspring, including but not limited to Cerberus, Sphinx, Chimera and Hydra. She also birthed Aikos with her communion with Zeus, which the child would later become Hades. Now, all of her children are completely different ( due to Typhon being the " Father of all Monsters "), they have one thing in common; violent and bloodthirsty, to different degrees and forms, yes, but still fundamentally identical. Now, one can say that it is possible that Echidnas possess the genetic code of everyone monster that has existed, most likely duw to tbe Demonic Energy acting as a " link" of sorts, and they may have took the role of main procreators during the age of old mamono as well. As for the siccubus's flight, their own physiological components are far more sturdy and efficient than a baseline human's, allowing for that even when the size would be in sufficient, and aerodynamically impossible. But, you can argue that they have a collective ability to levitate psychically, which honestly, would be possible with their naturally large magic reserves after the concersion era.