From Fiction (thanks Heran Bago) - A site devoted to otakukin, a premise so dumb that its existence almost defies belief. I said "almost", this is the Internet after all.
To be brief, and blunt, most Otakukin believe that they have the souls of anime characters, or at least come from worlds best represented by anime, or other modern fiction. Many Otas attribute this belief to reincarnation, although some have other definitions of their origin.
If that sounds like otherkins - the dopes who believe they are dragons or angels - I'm sure the resemblance is more than a coincidence. The idea that even one person feels they are the soul of an anime character trapped in a human body is so stupid it makes me want to choke a baby. How does a fictional character, something created in most cases by a committee of Japanese businessmen, end up trapped in the body of a fat teenager in Vermont?
Although you may be asking yourself how someone can be the reincarnation of a person that doesn't exist, for most Otas their identity hinges on the belief in multiple dimensions or words wherein other situations, including those depicted in anime, actually happen.
Oh, that explains everything! It's like Sliders only instead of another Nazi dimension there are like five dimensions where everyone is a hyperactive cartoon with a tendency to reveal their panties.