Those with ultimate skills can't be affected by lower skills:
"That fool thought he could control Milim. It's so impossible that it's hilarious. There's no way an insect like Clayman could do something that Guy never managed to do. Those who possess an ultimate skill are not affected by lower abilities. Every rule of the world is ultimately reduced to this unique level. In other words, they will not be affected by any form of magic―highest or not."
Stated again:
"Magic doesn't affect a person who possesses a Ultimate Skill. In a sense, this was the natural result because Ultimate Skills are of a higher rank of magic. But, it's effective even if it only gives an indirect effect rather than a direct one. In other words, weakening magic and the like wouldn't work, but giving support to an ally vanguard was effective."
Disintegration which isn't an ultimate skill destroys things at an atomic level:
"A power befitting a god. Though it's not an area attack, since it targets everything from the atom to the soul, it is considered the strongest anti-personnel magic. Upon completing the chant, a brilliant white light shot out from her hands. A blinding light. It traveled to the target at a speed of 300,000 km/s. Equal to the speed of light. The skill completely vaporizes the target via holy energy. The down-side―it requires a long time to prepare."
Spiritual beings can survive physical death:
"ÒÇîWe see, she may be dead, but she may live aganiÒÇì Ruminas pronounced her judgment after looking at the girl. This girl still has her soul. Two souls to be exact. ÒÇîReally?! Sis is alive?!ÒÇì ÒÇîNay, she is not alive. Nor is she dead. Death is but a state of the body; true death is the vanquishing of the soul. This girl still has her soul. So she is not deadÒÇì ÒÇîBut this is strange. Why did her soul not disappear upon death?ÒÇì Normally, a soul disappears when its vessel is destroyed. Beings like I can survive death of the flesh, but normal monsters and people are different."
Can't die unless a core break, which is soul destruction, is performed on him:
"Turn a body of flesh into that of a Spirit Form for a certain amount of time' That was the hidden power of God-tier armour.A Spirit Form, in other words, a God-like Being. Veldora was like that, and speaking of which, I was too. I didn't pay much attention, but it was certainly a state close to being immortal. Eternal youth was guaranteed, along with a strong degree of immortality. I couldn't die unless there was a Core Break or Energy Roast successfully performed on me. Although temporary, to be able to grant an existence of that scale, this armour was fearsome.But for this reason, it was not suited to half-Spirit Forms like Benimaru, and even less for true Spirit Forms like Demons.The armour had gone to where it belonged"
Demons who are spiritual life forms being stated to regen from physical destruction:
"Demons were a spiritual life form. Therefore, even if their bodies were destroyed, they would revive themselves through self-Regenerationn over time"