Magical Girl Lyrical Nanoha

The accompanying manga

• The manga take on the original series
• The A series
• The StrikerS series . You can find a review here
• The ViVid series (covering events after the third anime series)
• The Magical War Lyrical Nanoha series (note the change in title).

It's befriending time

I use "befriend" here in the traditional sense of the word, despite whatever Nanoha fans may tell you

• Nanoha Takamichi
  
  The titular character. We first know her as a ten-year-old child and follow her growth in body, mind and power well into adulthood. Like other Magical Girls (and anime protagonists in general), she has been living an ordinary life when a fateful encounter changes everything. Nanoha is cheerful, energetic, optimistic, in other words, a sweet happy child who is nice and a bit shy.
  
  However, velvet clads steel, as the saying goes. She has a strong sense of right and wrong, so do not cross her on that unless one has very good reason and prepares to meet the consequence (even before she discovers her magic power). A running gag in the fandom is that Nanoha will try to convince her opponents to avoid fighting, and when that does not work, she goes ahead blasting them into submission with firepower which is rather extreme for a Magical Girl series. Fortunately, in her universe, the losers do not bear grudge but end up being her friends and allies. Hence, in Nanoha fandom, "to befriend" means "to beat the crap out of" and everyone knows about "friendship through superior firepower". Nanoha herself is nicknamed "the White Devil", a reference to the original Mobile Suit Gundam series, because of her signature white-blue battledress and pink magic (the beam sabre of the Gundam RX-78 is pink). To take it a step further, you'll hear about her being the Gundam in the form of a girl.
  
  On the other hand, despite what some fans say, she is not overly eager for fighting. She always asks her opponents what they want to achieve, and she listens to others' advices. Nanoha also takes her power very seriously and indeed the first series centers around her thinking about what magic means to her.

• Yuuno Scrya
  
  The catalyst to Nanoha's discovery of her magic and the original owner of her intelligent device Raising Heart (but he is not really compatible with it. Thus he gives it up to Nanoha entirely). Yuuno is unlucky in that he spends half of the original series under the form of a ferret, effectively being Nanoha's pet. A very sweet boy who is less suitable for combat than the powerhouses around him, he is nonetheless not someone to trifle with (in general, a good rule of thumb in Nanohaverse is that being nice does not make a character weak. It makes s/he someone to beware of). Besides the healing ability typical of "supporting" character, he is top-notch at defense and magical control (he can teleport other people, forcefully if necessary. An feat considered really impressive by magi older than himself). A genius child of a tribe specializing in archeology, he is also extremely knowledgeable.

• Fate Testarossa
  
  Her strange name has its reason (well, Testarossa is a car brand. That choice of name has no explicit reason). Fate is Nanoha's rival the original series and later becomes her best friend. Yuuno introduces Nanoha to magic and its big wide world, but it's Fate who makes our protagonist question herself about her power and what she wants to do with it. She is even more powerful than Nanoha (and the latter is compared to a Gundam in ability of destruction), but is very soft-spoken and reserved (I did say that the nicer/shier a character is, the more reason to be scared of them).
  
  Fate has a lot of reason to angst and she does angst. However, she holds herself really well through the bad situations her fate (note the irony of the name) pushes her in. Like Nanoha, she goes through a phase of self-reflection about what she wants to do with herself.

• Other characters in the franchise (Warning: Spoilers)

Magic Systems and Devices