4chan was a great website at one point... Before the massive flood of "WE SEE MEMES, WE JOIN /b/, WE SPAM THEM EVERYWHERE" idiots. Then it became a massive meme-fest where the essence of 4chan was anally raped and tossed to the curb. Chris made 4chan to discuss his favorite manga/anime(s?), and /b/ (random) was thrown in there for the people who didn't always want to talk about Japanese stuff in the early years. It used to be a really fucking awesome place, but it got ruined... /v/ is the new /b/, but since it's summer, /v/ is ruined.
There are indeed porn boards. /h/, /u/, /d/ are some of the ones you WON'T want to visit... Well, there's 4chan for you. Some boards are still the boards they were designated as; /k/, /v/, /co/ (partially, because all the faggots ask for FFFFU- comics there), and /b/ because it truly is RANDOM.
Anime porn is hentai, which despite it's strange appearance, actually appeals to a massive quantity of people. It's really weird and is more of a niche thing.
And by niche I mean a select few people, sort of how BlazBlue appeals to certain fans of the fighter genre.
Also, BlazBlue is a great game. Try it out. Send KonnerDean a message on XBL if you wanna have a go.