Mahou Shoujo Lyrical Nanoha A's

Six months after the Jewel Seed incident, Nanoha Takamachi has returned to peaceful days while continuing her magical training and waiting to reunite with Fate Testarossa. That peace shatters when a red-haired knight named Vita attacks her and overwhelms Raising Heart with a strange cartridge-powered weapon.

Vita and the other Wolkenritter are collecting magical energy for the Book of Darkness, an ancient Lost Logia bound to a gentle girl named Hayate Yagami. Nanoha, Fate, and the Time-Space Administration Bureau are drawn into a conflict where the apparent enemies are fighting out of love rather than cruelty. As the Book nears completion, both sides must uncover the curse hidden inside it before Hayate and everyone trying to save her are consumed by its power.