Saint Quartz from mobile game Fate/Grand Order.
I made this using SketchUp by putting two positive tetrahedrons together. It's easy to design. The paint works requires some crafting skills that I don't have :( So I kept the colour of its material.
When you print this remember to generate proper rafts for this. The model does not need any supports.
The keychain model has not been tested. You can either try it or drill a hole in the first model :P