This is a type of item called a "water cup" or "yura-kira cup," which features a double-walled plastic cup with water, glitter, and a character figure inside. Double Structure: Water is sealed between the outer and inner walls, and when moved, the glitter and small figures inside float and sway. Main Uses: Primarily sold as cups for children, they are also popular as souvenirs and gifts in places like aquariums and character shops. I believe it's unused, but it's from about 15 years ago.