As mentioned on the History page, the world the players (and, in fact all of the Fleet) come from is simply one world in a great Many World multiverse of possible worlds. This was populated by an ancient race to study the development of life and of civilisation, and was observed and recorded by a processing core buried deep underground. It is from this setup that magic arrives.

Proto-human life on this planet was seeded with tiny, self-replicating nanomachines that would suspend throughout the body and send signals back to the underground core for storage. These were the 'silver tears' that many of the experimental magicians discovered in the course of play. By a stroke of chance, Esharia was one of the worlds on which a bug in this system was found: signals could be sent back to the core, that would then be relayed onto more of the nanomachines and produce a change in them. When humans discovered how to do this more or less on command, they called it what else, but magic. The use of blood in alchemy then occurred because the properties passed to the nanomachines suspended in that blood could be kept until they were imbibed and used.

The reason that other animals, plants, and non-organic materials were so much harder to do magic upon was that the nanomachines were not designed to work on them. The recycling of living material through decay and consumption ¹⁾ meant that some could be found, but not enough to cause as strong effect as you would get on a human.