After becoming Champion, head to Lumiose City and visit the Looker Bureau in the North Boulevard. This series of five post-game missions involves helping the detective Looker solve various mysteries around Lumiose City. These missions are story-rich and introduce new characters, culminating in a heartwarming conclusion. Completing them rewards you with valuable items and a deeper understanding of the city's underbelly. It's a must-do for any completionist.
