A Sentinel crystal is a small crystal of various shapes and colors measuring no more than a 8 cubic centimeters (~1 cubic inch). Some appear uncut, some smooth. Most are a singular color, while others a myriad.
Each one is a collection it’s previous owner’s memories, coupled with an advanced AI, language translation matrix, and life support capabilities. Each pilot names and shapes the AI to assist them in their journey.
In addition to the vast wealth of experiences and knowledge, the main capabilities of the Sentinel are apparent after transformation. The crystal expands, connecting the pilot into a direct neural interface, creating an extremely large engine of destruction. Each is shaped differently, shaped to the will and personality of the chosen pilot. Often, these take the shape of gods, heroes, and monsters of the chosen pilots homeworld, carrying weapons designed for starships and point defense. The DNI allows unparalleled reaction time and agility, even for the bulk and configuration of the Sentinel.
The crystaline structure heals damage on its own, is laser reflective, highly resistant to damage, and extremely flexible.
Pilots are chosen across the galaxy. Little is known about who, why, or how, but some cultures take it as a powerful omen. The crystals stays with the host till death. Crystals find their way back to their owner until their destiny is accepted.