Obtained: Speak to Urabe in Hee Ho Mart during the Chapter 4 Intermission.
To find the lucky object, she gives you the clue that it is inside the third door of the studio. Travel to the Idolasphere in Daiba Studio and teleport to LCD Panels: Door 2. Head across the panels to Door 3. A Treasure Key will be on the ground near the skull Mirage in front of this door. Report back to Urabe in Hee Ho Mart to complete the request.
Reward: Kiddie Candy