I did that speculative junk what I love to Steven Universe. Basically, gems look like semi-transparent hologram dolls with visible energy lines (sorta their nervous system?) and homeworld gems have almost robotic looking bodies designed for pure function and/or an alien aesthetic appeal. The Crystal Gems assumed humanoid forms a few hundred years ago so that they are less terrifying to humans. Steven has the glowy glowy nerves too, but his opaque meat body normally hides them.
Prompt on being immortal and or unable to die.