Six months after the Jewel Seeds incident, Nanoha is still using her magical powers to help the Time-Space Administration Bureau maintain dimensional stability. However, new adversaries involved with the dreaded "Book of Darkness" Lost Logia have appeared, wielding weapon systems that far outclass Nanoha's Raising Heart and Fate's Bardiche. Nanoha, Fate and friends must now find a way to match the strength of their new opponents and once again use their powers to prevent a large time-space disaster from happening – an event which threatens not only their world, but multiple dimensions!
In an era when ordering on the internet has become the norm, online vendors have a new favorite customer: Sakurada Jun! From voodoo dolls to x-ray specs, there's nothing this middle schooler can't get enough of -- until a strange package arrives one day. Inside is a sentient doll named Shinku, who is one of a special hand crafted set of dolls called Rozen Maiden. Luckily for Jun, not only does he get to keep her, but she's decided he'll be... her new servant?! Join Jun as he struggles to keep his sanity in a house full of dolls who all want his servant skills for themselves!
It's actually sort of difficult to explain why you would like both shows, but the fan bases for these two overlap quite heavily. Both the Nanoha and Rozen Maiden franchises definitely fall within the "magical girl" genre, but in many ways innovate past the genre's conventions and provide a similarly entertaining experience despite a lack of directly shared traits.
Lyrical Nanoha A's and Rozen Maiden appear on the surface as "girly" anime, but I personally think that they can be liked by any type of audience. There are enticing fight scenes, and the personalities in the characters are very likeable. There's an underlying plot that runs deeper than what they first present, and that's what I love about the direction in these two titles.
Following the events of the first television series, Jiyu Nanohana was happy; her days as Jubei Yagyu the 2nd were over, and she finally felt she could live a normal life again. However, when a clan of samurai calling themselves the Siberian Yagyu want revenge on Yagyu Jubei for their banishment to Siberia 300 years ago, once again young Jiyu is forced to take up the sword as the re-incarnation of the legendary swordsman.
Jubei-chan and Lyrical Nanoha are recognized for their magical girl stylings: an unwilling female protagonist, the wise sidekick who guides her as she takes her first steps into a larger world, and a mystical artifact that's the source of the heroine's power.
J2 and Nanoha A's are the epitome of sequels: the animation is slicker and the action sequences are much more elaborate. But be forewarned - while it is possible to enjoy the series on a purely superficial level, watching their respective predecessors will allow you to fully grasp the plot and see how these sequels improve on the original.