They are generally single, relatively well-off and physically weak - thus unable to defend themselves from assailants. That makes the otaku misfits who flock to Tokyo's Akihabara district rich pickings for the ruffians who have identified them as good targets for mugging.
Some years ago, Japan went through a phase of oyaji-gari - thugs grabbing wallets from old people. But seniors have become more careful. So the street hoods have turned their attention to another, newer sector of society.
Otaku is broadly translated as 'geeks' or 'nerds'. Although it was once considered more than a little embarrassing to be labelled one, they have since gone mainstream. Otaku represent a social movement that can trace its roots back to 1983, when the term was coined in a magazine article to describe the people attending a comic-book convention in Tokyo.
Their hobbies generally revolve around watching animated movies and television shows, playing computer games, reading manga comic books, collecting figurines of their favourite superheroes or making models of the robots that appear in their favourite films.
They are generally young and, as they prefer to watch physical activity on a screen rather than partake themselves, don't put up a fight when confronted. Incidents of attacks on them are becoming so frequent that Tokyo police have started describing the crime as 'otaku hunting' in their official reports.
And Akihabara is their preferred stalking ground.
For years, Akihabara has built on its reputation as the district of Tokyo synonymous with hi-tech electronics and gadgets. Its narrow backstreets are now packed with cafes where the female staff dress up like anime characters.