ooC: @Raka Jio's O-Part, Zero Type R, is a boomerang type weapon. It is a B rank O-Part. The main effect of it is that it forms blades based on an individual's hatred. Normally, it looks like a ring, but when he activates it, the blades form. Now, two people can look at the same thing and see two different versions of the the O-Part. One person could see small or virtually no blades, while another can see huge blades. It can be devastating to one person while being harmless to another.
Case in point, the following page is from the exact same time as the previous one I linked.
http://www.mangavolume.com/666-satan/chapter-666-satan-55/33
Jio's ally sees very tiny blades while the person he was fighting saw those giant blades from the previous link.
It's worth noting that everyone has some hatred. The only notable exceptions are the angels and demons of the series. Angels, on account of being angels, were considered innocent and pure. So no matter how vile they acted, they saw no blades. Demons were the exact opposite and always saw giant blades (even bigger than the previous link). Even someone like Jio will see giant blades on account of Satan being inside him.
It also has a secondary effect that allows him to multiple the effect of his left hand for his "Devil Summoner" ability. This is probably because it is related to his previous O-Part.
I hope this helps. I can also explain Jin's O-Part if you like. It's a much simpler effect, though.