The powers and capabilities of Aelyth are granted to a select number of creatures. Amid the physical realm of Yrell Aiene Tautom, the Kyusoakin are most noteworthy as the only Flesh Beings to receive Aelythian power.
Just as Dyiij had a hand in making Amonthe, therefore gifting him with the ability of supernal speech, she also was a major factor in the engineering of the Kyusoakin. It is a fact that is nearly forgotten over the span of the First Epoch, that when an Alyi grants life and consciousness to a creature, to an extent their Aelyth becomes part of that creature; and if that one goes on to produce offspring, they'll also have a share in the Aelythian powers that their parents received, if any.
In this way, the Alyi are interdependent with the universe at hand. When the beings they have created suffer, Fleshly or Spiritual, the Alyi suffers as well. Thus the Alyi are reminded of their own mortality.
Though the Xei and the Kyusoakin are connected to Dyiij, as they are hers, the Kyusoakin were gifted with more aelyth than the Xei. Hence their ability to manipulate themselves and the world around them in strange ways.
It is possible to gain the powers of a Kyusoa by either consuming all of its blood, or by sacrificing it by fire. The difference between these two methods is that sacrifices can be directed towards other beings than the one performing the sacrifice, whereas consuming the blood of a kyusoa grants the power only to the consumer.
Knowing this, Mokallai demanded Kyusoakin sacrifices from his worshipers, so as to regain his strength. Those who worshiped him and wanted power other than his (meaning the faux ability to manipulate 'destiny') were permitted to drink the blood of kyusoas. Though this granted them uncanny powers to an extent, they also came under a curse. Hence why Fylus appeared diseased.
The only way to abate the effects of the curse was to become possessed by an Iisae, as the renegade Agents of Death were capable of 'prolonging' death despite being as dilapidated, if not more so, than Mokallai. This, however, was limited only to the elect few that served as Mokallai's High Priests or Prophets.
Knowing of the Alyi's connection to the physical realm and the Flesh Beings within, Mokallai knew that he could, in fact, curse Dyiij herself by causing intense grief and turmoil to all living things on Dyjian. Especially in consideration that Dyjian is the only world that she specifically sees to, as it's the only one inhabited thus far. Therefore she's the easiest Alyi to kill, second only to Aischen.
Expansion and the Epochs
The Kingdom of Ecstasy Page 22