Obtained: During the Chapter 4 Intermission, speak to Arima who is standing across from the Idolasphere in Harajuku.
After you accept the request, make your way to Donadona in Harajuku and “Check” the door. Select the option to purchase the nasty Mustard-Natto-Yogurt Burger to trigger a cutscene. Afterwards, head back to Arima who will not be 100% convinced. Continue your search by speaking with the Female Staff wearing a maid outfit in front of Crepes Dia to try the Burnt Miso-Squid Crepe! Head back to Arima to share the news and complete the request.
Reward: Melmark x4 and new menu item at Cafe Seiren called Red-Wine Wasabi Cake