DETECTIVE OPERA MILKY HOLMES: ARSENE KAREI NARU YOKUBOU

The Phantom Thief Arsène is undeniably powerful. If she wishes for it, she could steal any treasure she wants without being caught or arrested. However, she pulls her punches because she desires that Milky Holmes achieve their full potential as detectives—and then to battle them without holding anything back. To achieve this, she tries every trick up her sleeve to create various situations for them to face each other—avoiding any hindrances that may come her way! — Description from AniList community (anilist.co).