GosickS is the sidestory volume of the Gosick light novel series. The first volume of GosickS, entitled The Grim Reaper that Arrives in Spring (春来る死神, Haru-Kitaru Shinigami), talks about the events before the first volume, from Victorique's admission to Saint Marguerite Academy in the year 1920, to the mystery that brought Kazuya Kujo and Victorique de Blois together for the first time.
- Chapter 1: The Traveler who Comes in Spring Brings Death to the School
- Chapter 2: An Ill Fate Befalls Those Who Tread the Thirteenth Step
- Chapter 3: The Ghost of Millie Marl Haunts the Abandoned Warehouse
- Chapter 4: A Golden Fairy Inhabits the Top of the Library
- Chapter 5: The Headless Lady Comes at Three in the Morning
- Prelude: The Reaper Discovers the Golden Flower