The dark hearts also can only absorb life force if given to it or take it if it comes in contact with a low tier life form like life spectres as the crystal form of the dark heart is considered powerful than life spectres. But it is impossible to absorb life spectres in most cases as life spectres dissipate much faster from bodies once the body dies. Providing life force would greatly weaken anyone unless by the way of necromancy. So the full form of the dark hearts hadn’t been ever seen, even by the dread twins.
An inferior copy of one of the creations of the dread twins’s, though the name they gave it to was Gemheart. The gemheart was found by a necromancer named Grudan after the dread twins left it in Zaura for it to get activated and so the old species could be brought back again. The gemheart could act like a soul seed and the dread twins were hoping to make a new species that was similar to the extinct species to which they belonged. But the necromancer started copying it and made inferior copies of it called dark heart to make a slave species for him.
The gemheart has the power to absorb, soul energy but unlike soul seeds which could absorb soul energy from soul realm it absorbed soul energy from dissipating souls around it, Dread twin’s hoped given enough time, it could form a soul and body of its own.
They even orchestrated a war so that the gemheart would have enough souls to absorb from but Grudan came across it during the war and took a curiosity towards it and found it to be really useful. As a result, he made dark hearts, but since those were inferior to the original they could only absorb souls through touch and as result the soul can be absorbed only by keeping it in contact with the dead body, preferably inside it. But since the dark hearts can’t absorb the whole soul essence before it dissipates, the beings formed all had only half souls and the creatures came to be known as half dead or Grens.
The dark hearts, however, was able to retain one of the original ability bestowed by the dread twins that there species possessed, a dormant life ability which allowed it to control bones. This enabled the dark hearts to form an exoskeleton around the dead bodies it fed on, the original race of the dread twins Vejelens also had the appearance of bone like skin. The Grens thus formed could move around because the dark hearts could control the bones and thus make it move.
Grens, even though it had the same mindset of Ghouls (formed by binding both souls and spirits in dead bodies) had one major difference, for some reason the bodies stop decaying and, as a result, it didn’t possess the nauseating smell of Ghouls.
The Grens could increase their soul energy like other soul spectres through consumption of soul essence but unlike the soul spectre’s its soul energy doesn’t dissipate until the dark heart is destroyed. So it is theorised by some that if they live long it would allow it to complete its soul join the living. But the process is considered to be very slow.
The dark hearts also has the ability to absorb spirit energy from the spirit realm, which meant it could retain memories, unlike ghouls which had only had fixed memories. But unknown to the dread twins, in the beginning, the spirit energy the gemheart absorbed from the spirit realm was from there own spirit vault which actually left their lair exposed to outside influence. So once the Grens complete themselves they could even visit the dread twins’ quasi-realm and even manipulate it like the dread twins. And if other ascended or their chosen were to come across this piece of information. They would be in danger.