User blog comment:Jopjopjop/Volume 18 Spoilers/@comment-69.244.232.185-20141011030726/@comment-25051741-20141019014133

The way Ishibumi has written the character, Cao Cao seems to me to be the most dangerous creature:  A Sociopath. He is a human that has lost his humanity. His true nature is best shown when he kidnaps and tortures the 9 tailed fox in front of her daughter. His complete and total disregard for the suffering of others shows his complete inability to empathize.

I do "get it" about Cao Cao thinking it is a Humans V Monsters war and devils, etc. are the enemy. However, just being of a different species (or origin) makes anyone fair game for whatever heinous acts he finds expediant. Remember he tortured the 9 tailed fox just to see if he could attract Great Red? If Cao Cao's plan had worked he was prepared to capture Great Red and the consequences be damned. Cao Cao was perfectly willing to destroy the underworld and probably this overworld as well just to satisfy his own need to test the limits of what it means to be human. I do not believe there is a definition of what it is to be human that can leave out the humanity.

I DOUBT ISHIBUMI WOULD WRITE IT THIS WAY, BUT:  It would be completely in character for Cao Cao to carefully kill off the girls and Issei's parents, one by one, in a way that could never be traced back to him, just to see what effect it would have on Issei's abilities.

Unless Ishibumi re-writes Cao Cao's character with a powerful "Come to Jesus" moment, there is no way he could be trusted and Issei will eventually have to kill him.