This is a reflector bracelet from NMB48 Team M. It faintly glows when light is shone on it. Perfect for those who run or do other activities at night or in dimly lit conditions. The size should be suitable even for those with quite thick arms. I tried it on myself (see photo 3) and it had plenty of room. You can wear it on your arm during Team M performances, and the bracelet will subtly glow when you're holding a penlight. It's quite eye-catching.