Obtained: During Chapter 5, talk to Urabe who will appear in Shibuya near the Lesson Studio.
She will give you a clue that the item is located behind the misty stage. After you have received the ability to unlock sealed areas during the main story mission (after Tiki wakes up in Chapter 5), head on over to Daitou TV Studio and teleport to Film Set B: Indoors (1F). Follow the path east and turn left around the corner to arrive at a barrier that can now be opened on the east side of the room. Once you break the barrier, the door will be marked with an “E” above it. After you enter the door, take a right and enter the door with a “N” above it. The item, a Treasure Key, will be located on the ground in this room. After collecting the item, return to Urabe near the Lesson Studio to complete the request.
Reward: Kiddie Candy