From Tasty.

These crystal candies by @mymanabites may look like gemstones, but they’re actually a traditional Japanese treat called kohakutou. Made with agar agar instead of gelatin, they’re crunchy on the outside and soft on the inside. This version hides a fun jelly filling in the center. They sparkle and shine, and they’re surprisingly easy to make https://tasty.co/recipe/crystal-candy-kohakutou