All studiers of magic have heard of the Mazoku, who fed off the negative emotions that plagued mankind. Few people have actually met one and survived. Fewer people have been able to say that they've met a Mazoku and say that he/she/it was not downright igly. And even fewer still could state honestly that they knew a Mazoku's long gorgotten nemesis, the Mazoku's sister race, the Israfael.
At frist glance, one would see no differance between a very human looking Mazoku and an average Israfael. The amount of power the two races possessed was about the same, too. However, the Israfael were the gentle yang to the Mazoku's violent yin. So when the Mazoku decided to eliminate them, there was nothing to prevent that from happening. The Mazoku hunted down the Israfael and murdered them in cold blood. Only one Israfael woman was rumored to have escaped death, but there was never any confirmation of that.
Rezo Akahoushii knew all of the above and much, much more....