Nullbreeds are the caretakers of Qatxis. Not much is known about their physiology, but there are some items the qat scholars were able to gather. Compared to other things discovered in Qatxis, there isn't much in the books regarding the nullbreed. And even the articles found in the books are alien and complex to understand, like the nullbreeds themselves. Most of the statements the qat scholars made are based on far-fetched ideas and theories.
Early in their study, it was clear that nullbreeds are created and not born. Further analysis suggested they are not sentient and can only do tasks they are told to do. This makes them closer to golems. But there are elements in their creation that can make them undead.
The only thing every scholar agrees on is that the nullbreed are created, but the words "gene-splicing" and "in-vitro" are more exotic than the nullbreeds themselves. It is a fact that they are made from something, and their creation process results in the same individuals.
The other fact is that they don't have a will of their own. There aren't many nullbreed in Qatxis, but the qats marked them with different colors to distinguish them. After the coloring, they discovered that the same nullbreed does the same daily job. Mostly they do nothing else but clean, but it is always the same nullbreed that cleans one particular building.
And this is where the far-fetched theories come. Nullbreeds do not eat, drink, or sleep, and their skin is impervious to heat and cold. These results came after empirical testing. In theory, if the dots on the Treeverse are truly other spheres, the nullbreeds would be ideal for traveling between the spheres. They don't require anything; when they arrive, they can build a base and plant a Hopper tree to connect the spheres. Unfortunately, this can't be tested because they do not speak, and the qats could not change their daily routines.
Mrrr orr-ow…gene… HISS