Touhou

    Touhou is, quite simply, hellish! Imagine combining the difficulty of I Wanna Be The Guy, Gradius, and Tetris in one game. Now, make about 12 more games like that, and you've got Touhou the main-series Touhou games. Basically, you fly around as one of two to, in some cases, ten magical girls and dodge bullets while returning fire. There can be anywhere from dozens to, in some of the more dire examples, HUNDREDS of bullets on screen at any given time, depending on the level, the game, and the difficulty. (It's called "Lunatic" for a reason, people! There can be upwards of a THOUSAND bullets on-screen in some cases!)
    In addition to the bullet-hell games that make up the main series, there's the first game, which is really more of an Arkanoid clone, six spin-offs, of which three are Street Fighter-style fighting games (four if you count Hisoutensoku, which is a stand-alone add-on for Scarlet Weather Rhapsody, which is the second fighting game and third spin-off), two bullet hell-style games where you defeat your enemies by taking pictures of them (Note: I am not particularly fond of either of them), and Fairy Wars, which takes the formula for the main-series games and shakes it up a little, creating a game which only Chuck Norris can beat with 0 deaths. Furthermore, there are a few hundred fan-made games in almost every genre of game imaginable, and that's just the more well-known ones. On top of that, there are MODS for unrelated games (including Civilization IV and TF2) that allow one to play as characters from the series.
    Now, while you may be thinking that, while the majority of the characters in the games are female, there must be five or six men, I have news for you: There are only two (confirmed) males in the games, and they are a turtle who disappeared after the fifth game in the series, and a pink cloud... man... thing. Additionally, while the turtle is part of your sprite in the games in which he appears (at least, he is if you choose Reimu, who is the main character in the series and appears in all but two or three spin-offs), neither of them is really a playable character and really take something more along the lines of support roles.
    These games are known for being bigger meme fountains than Pinkie Pie, and the fanbase tends to make TONS of remixes of the music. By that, I mean that there is a torrent out there consisting of a good portion of the remixes available on CDs (usually sold at Comiket, but often available for purchase online) with a total size in excess of 1.2 TERABYTES, with that number growing as the maintainers add MORE stuff to it. For comparison, a 45-minute album at 320 kbps is approximately 138 MB. Additionally, if you were to attempt to download all that data on a dial-up connection, your download would take several CENTURIES to finish.