In the time before time (no, not the LAND before time, Littlefoot), After the war between the Gods and the Primordials had mostly ended, a great crystal gate was created at the edge of the stars to keep that which was Outside from ever invading this realm. Creatures from beyond reality were not meant to dwell hear, and there are tales that this was something even the Gods & Primordials agreed upon.
But that was a long, long time ago, and things are very different now.
At some point, the gate was shattered. Of course, nobody was out there, so no one is exactly sure when or how it happened. There are theories that it was tied to the Great Cataclysm, there are theories that it was a some evil chaos god enacting a master plan of destruction, there are even theories (mostly among dwarves) of poor architecture and natural wear. But for whatever reason, the gate shattered into a billion shards of fragmented reality, spewing through time, space, and the void.
But the gate was not just a physical or magical barrier. It also had great intent put into it. When the gate shattered, that intent translated into will, which was now free. That free will manifested in some places where gate shards crashed to earth, and sentient crystalline beings rose up as a result. Those beings are known as Shardminds.
Beyond that, most regular folks don’t know much else about Shardminds. They’re quiet, they don’t breathe or eat, and they don’t sing or do things that “normal” folks do. Many people see them as golems, except made of crystal. But they are so much more.
Shardminds are self-aware constructs formed of pieces of the broken reality gate. They can communicate telepathically with creatures near to them, and they have many questions themselves as to why they exist. That they represent some sort of failure to do their original duty is a common thought among Shardminds, but their truth may be far from that manufactured guilt.
Known to have great proficiency with magic and psionics, the silence of shardminds has also given them the ability to be very good rogues and assassins. Against Outsider threats like Aberrants, Shardminds are vicious beyond belief, completely obliterating these foes whenever possible.
There is a small sect of Shardmind who believe that the Gate was destroyed because some ambitious shards sought to be free, and that the Gate can only be restored if all sentient Shardminds are destroyed, their essences allowed to flow back to the Reality Gate. Most Shardminds just KNOW this on some deep level, maybe through a low level shared telepathic field or some morphic field of some sort… but they don’t tell other races about it. Imagine the experiments wizards might try if they thought a Shardmind could be used to ward against Aberrant creatures. Or the witch hunts that would begin if Shardminds were painted as willful destroyers of the Gate in human communities. Not good.