Magical Girl Lyrical Nanoha A's

Magical Girl Lyrical Nanoha A's (魔法少女リリカルなのは エース) is a thirteen episode anime that aired between October 1 and December 24, 2005. It is the sequel to Magical Girl Lyrical Nanoha and thus, the second entry in the main Nanoha continuity.

Story
Six months after the end of Magical Girl Lyrical Nanoha, Fate is returning to Midchilda to stand trial while Nanoha returns to the life of an ordinary girl. However she is attacked by a mysterious red knight that serves as one of the guardians for another of the Lost Logia, the Book of Darkness. This blank tome must be filled with magic drained from mages' Linker Cores and the spirits of ordinary living beings in order to be completed, otherwise it constantly drains the health of its current owner, Hayate Yagami. As old friends reunite to deal with the new threat, they discover the truth behind the Book and its troubled history with the Time-Space Administration Bureau.