Gamera Magatama

See also
https://sketchfab.com/tochigimaibun/collections/komochimagatama-found-in-tochigi-d589aed3bf4145c2b2266ea80610bb2e
and 
https://www.yourprops.com/Magatama-pendant-replica-movie-prop-Gamera-2-Region-shurai-1996-YP806668.html

I based this on the above “yourprops” link's photos, I feel like it's pretty close if not 100% screen accurate. In the first of the 90's Gamera trilogy it's metal or glowing red/dark brown when active. I printed mine rotated nearly upside down to minimize supports, as seen in the 3mf file. If you're cosplaying it might be a better idea to remix this and create a two part mold for casting in epoxy or silicone, you could embed some led lights with wires hidden in the chain or something. 

The textured version has a slight texture (natch) which might make it look nicer when printing in matte filaments, the smooth version seems to do better with sparkle/bicolor filaments. Play around with them, both models are included in the .blend