#1 - LOLITA
Lolita isn't just a weird 50s novel, it's a solidified fashion trend that has become globally recognized. Starting in Japan (as most things do), Lolita fashion is a bold reaction to the overly sexualized treatment of women. Where most popular culture focuses on skin and being sexy, Lolita is characterized by knee length petticoat skirts, high collars, feminine patterns, and layers. The focus on women feeling “cute” or “kawaii” may seem childlike, but in fact it is very empowering to many women. Examples of Lolita style are very evident in Anime, Manga, Cosplay, and many video games. There are many different subsets of Lolita, from cute to gothic and it's easy to get obsessed.
Wait, I'm familiar with mlp, I had those toys in the 80s and I think there was a cartoon...
True, but the new version of the show isn't just popular with young girls, the biggest fans are men in their teens, 20s, and even older. They call themselves Bronies (brother ponies) and they have a huge online community that is heavily focused on pony apparel and bizarre kinds of fan art. They have become so popular that even the creator of the show embraces them. Adult My Little Pony fans may seem scary at first, but my experience with Bronies has been positive.
Homestuck is a webcomic created and produced by Andrew Hussie. The series is about a group of teenagers who install a beta copy of a computer game and unknowingly bring about the end of the world. They're transported to another world called Sburb and encounter Trolls. Trying to explain the plot is futile, so you'll probably need to go experience it yourself.
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The following group has earned a bad rep because (thanks to CSI & MTV) Furry is often seen as sexual fetish. While there is that undeniable aspect of the subculture, most Furries are people who appreciate anthropomorphic animals. Basically this is a fandom filled with animals that show human attributes like talking, wearing clothes and walking on two legs.
The fandom is known for high quality fan art, written fiction, and of course, the fur suits. Each Furry has their own “Fursona” which is the animal version of themselves. This is how they communicate with other fans. Furry conventions have been going on since the 80s and aren't going to lose momentum any time soon.
#5 - FREE!
This was a new one to me, but I instantly saw the appeal. Swimming Anime started as a 30 second commercial by Kyoto Animation to showcase the capabilities of their studio, nothing more. The video featured four strapping young men on a swim team. As soon as the video was released it went viral and in less than 48 hours Tumblr etc, was flooded with fan art and oh so much fanfic. The ridiculously popular petitions convinced the studio to make Free! a full fledged series and fan girls everywhere rejoiced.