To get the Chaos Key, you need three items they are the Macroman, Tarot Card, and the Ramen. The Macroman is found in the NW corner of Ygdra Canaon. The Tarot Card is found at Basil Gate in the SE corner, there is an X made of grass. The Ramen is in the grate on the front car on The Magical Train. Go to Kerachi Village, go to the tavern and talk to the colector.