The Rainbow Undecimber (무지개빛 십삼월, 무지개빛 十三月, Mujigaebit Shipsamwol; "Rainbow-Coloured Thirteenth Moon") is one of the 13 Month Series created by legendary craftsmaster Ashul Edwaru for the Princesses. It has never been granted to a Princess. Unlike most of the weapons that form the 13 Month Series, the Rainbow Undecimber is an Arms Inventory.