Magical Girl Lyrical Nanoha A's

Summary: 

    A's is set six months after the first series and begins by explaining what has happened in the time between the two series. Fate, Yūno and the rest of the Time-Space Administration Bureau return to help Nanoha combat a group of mysterious knights from another dimension called Belka. The knights serve a wheelchair-bound girl named Hayate, whose health will deteriorate until they complete an artifact called the Book of Darkness at the cost of the magic and spirits of civilians. The thirteen-episode series also introduces another new character, Gil Graham, and explains what happened to Lindy Harlaown's husband.