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Magical girl (Japanese: 魔法 少女, Hepburn: mahō shōjo) is a subgenre of Japanese fantasy light novels, manga, anime, and video games which features girls who use magic or possess magical powers. Magical girls transform to unlock their powers and are often accompanied by an animal mascot, using wands or scepters as a weapon to fight monsters and the forces of evil. 
History of the Genre
Manga and anime historians regard the Princess Knight manga, released in 1953, as the prototype for the magical girl genre. Himitsu no Akko-chan, serialized nine years later (1962) in Ribon, is generally accepted to be the earliest magical girl manga. Sally the Witch, adapted from the manga of the same name, is regarded by historians as the first magical girl anime. Sally the Witch was inspired by the Japanese dub of the television series Bewitched.
Originally, all Magical Girl shows were produced by Toei Animation, so "Magical Girl" wasn't so much a genre as a Series Franchise. This lasted until Ashi Production's Magical Princess Minky Momo hit the airwaves in 1982. The first instance of a magical girl team was a crossover in 1987 between Studio Pierrot's four '80s Magical Girl shows (Magical Angel Creamy Mami, Persia, the Magic Fairy, Magical Star Magical Emi, and Magical Idol Pastel Yumi. 
The Magical Girl Warrior subgenre, despite being the most well-known style of Magical Girl show in the west, didn't hit until Sailor Moon in 1992. This was essentially a combination of the earlier style shows with the superhero genre. Sailor Moon was a huge hit, and, naturally, other shows were made in the same style.
The wave of shows inspired by Sailor Moon eventually subsided, but new sub-genres spawned soon in its wake. As of present, most magical girl shows can be loosely organized into three broad categories.
Neo-classical, codified by Cardcaptor Sakura. Essentially, old school magical girl coming of age stories updated with the sensibilities of the modern age and the roles of girls and women in it. Mainly aimed towards young girls but often with a significant peripheral demographic of adult males. Contemporary examples include Ojamajo Doremi, Shugo Chara! and the Pretty Cure franchise (though that also fits in the second set).
Action Hero, created by Pretty Cure, but codified by Magical Girl Lyrical Nanoha. Magical Girl Warrior territory, with emphasis on "Warrior" and often enough Hot Blood to put a Shounen fighting series to shame. Largely aimed at the teenage and adult male demographic, and as such placing heavy emphasis on Fanservice. The Improbably Female Cast is frequently used as an excuse for Les Yay. Examples include: Mai Hi ME, Vividred Operation, and Senki Zesshou Symphogear.
Deconstructive, codified by Puella Magi Madoka Magica. Debunking the very concept of a world where young girls are forced to confront evil as a Crapsaccharine World with plenty of dark secrets and delving deep into the psychology of its cast, often with religious or philosophical references. Madoka itself was considered the equivalent of Neon Genesis Evangelion and Berserk for the genre. Other notable examples include Princess Tutu, Il Sole penetra le illusioni, and Yuki Yuna is a Hero.
Of course, there are other examples that feature similar themes but diverge even further from the old-style shows. Many fans felt that shows such as Magic Knight Rayearth were still Magical Girl shows, despite all the dissimilarities from the previous generation (others disagree, and feel that Rayearth is Shoujo RPG World Fantasy instead).
The magical girl genre emerged as a direct result of the surprise popularity of Bewitched with a generation of Japanese schoolgirls. Samantha is the archetypal magical girl, conventionally attractive, traditionally feminine, with tremendous power tightly constrained within a limited sphere, and subject to the anxious masculinity that hedges her into that sphere. She can–and frequently does–assert herself, but ultimately she is trapped by the limitations of the norms of television in her time, bound to perform femininity with perfect makeup and hair, cute dresses, and a socially approved role as a wife and mother.
...By Sailor Moon, the norms of the genre were largely set. Magical girls, like witches, gain their power from otherworldly sources, whether granted by the ruler of the Mirror Kingdom, accidentally released from a mysterious book, or inborn as a result of their past lives in the royal courts of the Moon. Magical girls, like witches, have their familiars, sentient creatures taking on animal form. And of course, magical girls, like witches, wield tremendous and varied magical powers.
But curiously, those powers are always directed at enemies as otherworldly as the magical girl’s origins–indeed, often the enemies are tied intimately to those warnings. As a general rule, magical girls do not fight government corruption, corporate malfeasance, or even that mainstay of the masculine hero, street crime. Their power, in other words, not only comes from the fantastic, but can only be directed against the fantastic....The power of the magical girl is usually sanitized in two ways. First, as already mentioned, her power is not permitted to impact anything the viewer might recognize as part of reality, but is instead almost invariably focused on fantastical opponents. Second, she is made to constantly perform femininity (remember, the counterpart to hegemonic masculinity is performed femininity), with frilly or skimpy costumes, elaborate poses, and of course the nude dance of the transformation sequence all serving to remind any potentially intimidated male viewers that she is still subject to the male gaze and still submitting to the social norms of the “good girl.” 
As costumes and special outfits play an important role in most magical girl anime, they are subject to intense appreciation, debate, and criticism from both fans and casual viewers.
Ok so, here are the 3 rules. They are in no way absolute, they are heavily subjected to my own arbitrary taste, and they probably don’t even capture the full extent of what a good outfit is, but for all our intents and purposes, they are a good guideline so, in no particular order, without further ado:
Rule 1: The outfit must look appropiate to the user’s body and viceversa. Rule 2: The aestethic of the outfit must be concise.Rule 3: The outfit must look comfortable to move/fight with/ appropiate to the user’s combat style.
- Magical Girl Fashion- The 3 Basic Rules by shizukateal.
-  Wikipedia: Magical girl (Accessed March 21, 2020)
-  Tvtropes: Magical Girl (Accessed March 21, 2020)
- Gradually and indirectly, over time, gain in political significance (I’d Never Allow That to Happen) by froborr, March 26, 2013.
- Tumblr post by shizukateal.