Scar's Realm is a place that you can only access if Scar takes you to it. The reason that only Scar can access this realm is because it is a place in Scar's mind that is bent to her will. Whenever Scar summons her katana blades or summons anything from thin air, it all comes from her realm. When Scar gets mad or needs alone time, she can physically transport herself into her realm. Scar's realm is where the Sacred Music Box of the Sky Kingdoms is held, so no one else can unleash more danger in to the mortal realm(Earth).