I don't like anime. You may have noticed. It gives me a general skeevy feeling everytime I see those giant eyes and impossible hair that anime characters have. Someday I might try to sneak into an anime rpg just to see what this creepy underbelly of rpg culture is like. Before I do and, perhaps, before you do, here are some terms to be aware of:
Bishounen: (Or Bishonen) This means "beautiful boy." This is when a male character is very feminized. He may be homosexual or just very girly. A character like this is often very smart, creative and sexual but not usually in an aggressive or offiensive way. But do not be mistaken: Gary Stu's run this category. They are all terribly witty and have martial arts abilities. The Mary Sue equivalent is "Bishoujo" even though it's redundant because Mary Sues are always beautiful.
Chanslash: (Also known as 'shouta' or 'shota') The word "chan," used as a suffix, is an affectionate Japanese term for children. When coupled with the word "slash," it means underage sex. Both or one of the characters involved in sexual activities is a child and they can be horribly graphic. Normal slash communities tend to find this stuff offensive and encourage those involved to clearly mark that a story or rpg contains chanslash but you may not find it until you stumble into it.
Ecchi: In Japanese, this is how the letter 'H' is pronounced. 'H' as in Hentai. It's a wink, wink, nudge, nudge way of getting around this word.
Henshin: The act of turning into a magical alter ego. Your dull character of Elsie Horace puts on a magical necklace and her mousy, brown hair and hazel eyes disappear and she turns in Mary Sue with waste length blonde tresses and shimmering, purple eyes and she can fight crime with her rapier wit and sharp katana.
Hentai: This refers to extremely kinky sex and horrific levels of porn. Perhaps porn that even the most seasoned of horndogs might shudder at. Also called "tentacle porn," like chanslash, this stuff should always be clearly marked but isn't always. Participants in hentai can be gay, lesbian, straight, young, old, human, vampire, dog, cat, squid, alien, plant, park bench, resident of Delaware or whatever sort of filthy kink combinatination you can come up with.
Ketsuekigata: This means a universal knowing of what someone is all about based on knowing just their blood type. I was going to make fun of this because I assumed it was just a comic book thing but it is taken seriously in Japan. Have a look here! Then again, when you calculate all the possibilities such as vampire, werewolf or whatever blood, you get a whole new set of rules that make this theory lame.
Lemon: This refers to a porn-heavy level of hentai. This is the hardcore stuff that will blow your mind.
Lime: This is a mild level of hentai that might be okay for some audiences. More stuff is suggested or happens "offscreen." There's still sex but it's mentioned in a PG-13 way.
Yaoi: Male on Male action! HoYay! Harry/Draco, Draco/Ron, Ron/Neville, Hagrid/Dobby, Angel/Spike, Warren/Andrew, Kirk/Spock, House/Cameron, Charlie/Sawyer, Edward/Jasper, J.D./Turk, Tony/Silvio... You get the idea, right?
Yuri: Female on Female action! Hermione/Luna, Buffy/Willow, Britney/Christina, Bella/Esme... and so on.
This is just the tip of the iceberg. Anime is a strange and silly world and the stranger and sillier it gets, the more insane the sexual situations are. More definitions are on the way though it may kill me to look at more of this crap.