This is a cushion cover, pillow cover, towel, or cloth.
Index from "To Aru Majutsu no Index" seems a bit surprised to find herself on both sides of this super-big pillow cover! The pillow cover measures 150cm by 55cm, and is made of 95-percent polyester and 5-percent polyurethane for two-way stretch; it's the perfect size for the included pillow, which is stuffed with 100-percent polyester for maximum softness and huggability!