Edenia, man, there is actually two of them! I think you may have to complete Konquest Mode first though.

Jade: In Edenia in a Tent. Find Rain and Talk to him. You Be Asked to find a cave. go to G-8 and you'll find a Cave there with Jade in it. She tell you to bring rain go back and tell rain and he runs off...then go back to that area and rain is dead on the ground Jade is standing next ot him talk to her there. Jade will stay there from that point on onward, where you can train with her. there also another Jade back inside the tent as well a glitch probly. (Just make sure to talk the correct Jade next to Rain Body)