Obtained: Speak to Urabe who is the student standing in front of Anzu in Harajuku.
Head on over to the 106 Idolasphere. Starting at the entrance, take the first right and go into the sleeve of the blue mannequin. Head straight to the position switcher and select the right switch. Turn around and go back into the sleeve. Head to the position switcher on the right and select the middle switch. Again, head into the sleeve. You will notice that this level is 2F and it says green park on the wall so you know you’re in the right spot. Head forward past the trees towards the magenta wall and turn left following the path. Just before the pink mannequin, turn left and head a short ways forward. Take the first available left. The Treasure Key will be in this corridor on the ground under the trees on the wall. Once you collect the item, head back to Urabe in Harajuku and speak with her to tell her that she made another accurate prediction.
Reward: Kiddie Candy