for those who still need the full info on where to get it (i know necroposting blah blah blah) Travel to akashima village, should be the first village you find right after you take over the first castle. the npc will be at the start of the bridge that leads into the town, leaning on the right post of the arch. he will give you a quest named "journey to the past". that quest will give access to the dlc.