Signum

Nanoha A's Signum enters the story when Vita has attempted to steal Nanoha Takamachi's Linker Core (a mage's source of magic) for the Book of Darkness. Since the arrival of Nanoha's cavalry, Fate Testarossa and Yūno Scrya, Vita is cornered and Signum must come to her rescue with Shamal. The Wolkenritter overpower the TSAB troupe with their use of high-powered magical cartridges, and Signum manages to snap Fate's staff, Bardiche, in half. The battle ends with Shamal finally managing to get Nanoha's Linker Core and Nanoha breaking Vita's barrier. Signum refuses to take a bath that night for fear of Hayate seeing the injuries sustained in her battle with Fate.

Signum may appear emotionless, but she is completely dedicated to Hayate, and as the leader of the Wolkenritter, fights for the others as well. The Wolkenritter attack mages to steal their Linker Cores, their sources of magic, to fill the 666 pages of the Book of Darkness with this power before it saps any more of Hayate's and she becomes fully paralyzed.

They continue to obtain Linker Cores and fight off interference from the Time-Space Administration Bureau (TSAB), mainly Fate- with whom Signum faces off during every battle, and whose strength she respects- and Nanoha, while they try to keep Hayate from knowing that they are stealing magic for pages; she has told them that as long as she is mistress of the Book, she will not allow anyone to be harmed over it. Signum, determined to save Hayate even if it means going against her wishes, convinces the other Wolkenritter to fill up the Book of Darkness anyway.