You could buy this for your Lv.20 NIN and spend a handful of gil, or you can go to Dangruf Wadi with a vial of Fresh Blood, trade it to the ??? and kill the Chcocoboleech to get the Gassan which is a 100% drop off the NM, and does the same damage with the same delay as the Ganko for Lv.15 NIN. Your choice.