what is natural kei?

Natural kei is a fashion that sprung up in Japan in the 1970s. It has a period, pastoral look-- like something from another time. Above all else, this style promotes being natural and feminine.
The ideal, romantic lifestyle and period fashions from Western literary classics such as Anne of Green Gables, The Secret Garden, Rebecca of Sunnybrook Farm, and Little House on the Prairie were most likely one influence on the creation of natural kei because those series were very popular with young Japanese girls around that time. To illustrate the point, here’s a side-by-side comparison of Anne of Green Gables and an outfit from the natural kei brand, Garland.
Additionally, in the 1970s and early 1980s, the "prairie-revival" look was popular around the world thanks to brands like Laura Ashley, Gunne Sax, and Young Edwardian. Designers borrowed ideas from the kind of dress worn by hippies and flower children in the 1960s and thus made long period-inspired dresses the popular style.
Besides the prairie-revival, trends such as peasant chic, Neo-Victorian, and Neo-Edwardian style also had a big influence on popular Western fashion, so it's possible that natural kei was influenced by these clothes as well.
Of course, there are probably many other influences responsible for the genesis of natural kei, but it seems as though romanticized period clothes from western countries was the main impetus. Kaneko Isao, designer of many brands and once the foremost designer of natural kei fashion, commented that one of the reasons he first started designing clothes was because he "liked America" and was inspired by the fashion he saw in American and European films of the time.

Some characteristics of natural kei:
1) Lavish but understated embellishments. A natural kei dress may appear plain from a distance, but a closer look yields extravagant details such as quilting, pin tucks, self-ruffles, embroidery, tiny lace edges, covered buttons, etc. Many times, these trims have either been created out of the same fabric as the dress or specifically dyed to match the dress fabric.
Since embellishing techniques like these can often be lost to the eye unless you're close to the garment, perhaps that says something about natural kei-- that its meant to make the wearer happy and not so much meant to impress observers. It also adds a real feeling of luxury and femininity.
2) Lots of layers. For example, in a proper natural kei ensemble, you could wear a first layer-- an underdress or underskirt and blouse-- followed by the second layer-- a dress-- and then an overskirt or apron, and finally a cardigan, vest or jacket on top of all that. 
Each of these layers is yards and yards of fabric, made even heavier by all the pin tucks, ruffles, and other embellishments. Unlike lolita fashion, any volume seen below the waist is created with layers of clothing rather than petticoats. Thus, there's no false volume and it leaves an impression of depth and softness.
4) Lack of body consciousness. Clothes are worn loose, often but not always with a relatively undefined waist. Most natural kei outfits are long and have a modest neckline as well.
Sometimes the knee-jerk reaction to outfits like these is that they're frumpy. It's true that natural kei is not in tune with modern fashion or the idea of using clothes solely to flatter one's figure. But girls who wear natural kei wear it for themselves because they enjoy it, so advertising the shape of their bodies isn't a priority.
5) Solids, motifs, and prints. Solid colors are used a lot, but there are also many stripes, florals, and plaids present in natural kei. Some common motifs for prints are wreaths, vines, hats, food, berries, flowers, and bows, but I've also seen rather over the top prints that include teddy bears, bunnies, goldfish, and even kewpie dolls. 

Brands such as Pink House, Wonderful World, and Kaneko Isao usually have the more unusual prints.
6) Natural-looking accessories. Shoes are usually clunky sandals, clogs, oxfords, mary janes, or boots that look comfortable and ladylike. Natural kei girls don't generally wear high heels or overly delicate shoes. Bags are basket bags, plain totes, leather satchels, or purses made of printed fabric that match the dress. 
Brooches made of dried, silk, or paper flowers can be used to pin a scarf or handkerchief along the shoulders or just be pinned on one side of a blouse like a corsage. 
7) Romantic hair and makeup. Natural kei hair styling looks pastoral and natural, usually with braids, loose curls, or waves that frame the face.
Sometimes girls wear straw hats, kerchiefs, or floral corsages and wreaths in their hair to embody the stylized prairie look. Makeup is kept natural as well, with rosy cheeks and lips and simple eyes.

Here are a few of my favorite brands that carry natural kei clothes:
1. Garland
Garland was a brand focused on simple dresses and skirts sometimes accented with pinafores. The style really reminds me of Anne of Green Gables.
Garland clothes had a very natural and fresh look, like something a girl living in the country would wear.
Even though Garland closed a few years ago, you can still find some pieces in Japanese consignment stores or web shops, as well as online auctions. 
When it first opened in 2002, Excentrique sold mostly corsets. The brand has been getting more attention for lolita and otome clothes in recent years, but it also makes some lovely pieces that would work for natural kei. 
There's a definite historical influence here, as seen in this white blouse and brown smock dress; notice the lovely pin tucks along both bodices.
Seraphim is a brand that often carries natural kei pieces. It features elegant lines but also includes nice little details like the pin tucks, pleats, and ruffles seen here. 
Notice the contrasting material on the collar, cuffs, and covered buttons of the dress on the left, and the elegant rose pattern and velvet ribbon waist detail of the dress on the right.
4. Sincerely
Sincerely doesn't get much attention as a natural kei brand, but it's been around since 2005. The website says the brand aims for a late 19th century British look or one from the Meiji and Taisho eras in Japan.
The "Jane" line available in the web shop was named after 19th century British literary heroine Jane Eyre, so it's supposed to have a stylized "governess" feel.
5. Fairy Wish
Fairy Wish was started in 2003 by designer Alice Kobayashi. It often features Sachi from the band Kokusyoku Sumire as a model.
Fairy Wish does offer lolita and otome clothes, but the natural kei items look beautiful as well. The cuts are simple and elegant.
6. Pink House
Finally, the most famous natural kei brand of them all, Pink House. It was founded in 1973 by the designer Kaneko Isao and became popular in the mid-80's. He also started Wonderful World and a self-titled brand called Kaneko Isao in 1990. Kaneko stopped designing for Pink House when it was bought out by a larger company in 1994. When Kaneko retired in 2007, his brands Kaneko Isao and Wonderful World both closed for business permanently, but Pink House continues to produce beautiful natural kei garments. Here's a look at some Pink House coordinates:
As seen in the outfit to the right, more formal Pink House coordinates are lavishly embellished and layered, but there are also more informal ways of wearing Pink House clothes, as seen in the outfit on the right.
Even though Pink House has been around for such a long time-- well over thirty years-- and its popularity has definitely peaked, it's still worn in Japan mostly by housewives and some older ladies. I hope that someday a younger audience will become interested in Pink House clothes again.