Simple two-part model of a shulker box from Minecraft!
Just print the two part and they slide together in a twisting/screw-like motion like in Minecraft. There's also a small cavity where items can be placed inside the shulker box.

No supports required! Tolerances are fairly loose and the model should still work fine scaled up or down (though I haven't tried myself). Images are printed using GEEETECH Silk Purple PLA.