Magical Girl Lyrical Nanoha-5
Earth is but one world, one dimension among many. Across the dimensions, the Time-Space Administration Bureau maintains the peace, hunting down dangerous artifacts and ensuring that worlds develop at a safe pace. Their goal is to prevent the destruction of innocent worlds, whether they know of dimensional space or not. A noble goal, one that frequently faces the threat of Lost Logia, artifacts of great power, being misused.
Into Earth come several of these Lost Logia, resulting in a young girl being introduced to the world of magic. A girl with great potential, who only wants to help hunt down these dangerous items. Until one day she runs into another girl, just as desperate to collect them, just as powerful, just as young and kind. And that girl says to her, "Please, won't you help me save my sister?"