I'll let Wikipedia tell you what Otakon is all about:
Otakon is a fan convention in the United States focusing on East Asian popular culture (primarily animé, manga, music, and cinema) and its fandom. The name is a portmanteau derived from convention and the Japanese word otaku. Otakon is traditionally held on a Friday, Saturday, and Sunday in late summer at the Baltimore Convention Center in Baltimore, Maryland's Inner Harbor district. It is considered the second largest and one of the longest-running Anime conventions in the United States.
There was a line, which had been there since morning, wrapped around the Center, with people waiting to pre-register. I saw this young man tonight on my way back to the Light Rail station, just across the street from the Convention Center, and he was gracious enough to pose for me.
Now to badly paraphrase Justice Potter Stewart,I don't know much about animé or manga, but I know a great costume when I see one.