Otaku is an old formal second-person pronoun built from taku, house or home: literally 'your household.' In 1983 columnist Akio Nakamori branded hardcore fans with it because they addressed each other in that stiff, distancing formality. The label stuck to the subculture.
The story of the panic: in 1989, after the Miyazaki Tsutomu murders, reporters found his room stacked with videos, and otaku became a national fear-word, the loner sealed in with his images. The word spent the nineties as a diagnosis and the two-thousands as a pride flag, train otaku, idol otaku, voice-actor otaku.
The claim: the word is a confession, the fan is addressed as a house because the self never leaves its room. Extend it and otaku merges with hikikomori, the documented shut-in phenomenon, into one syndrome of a society that replaced the village with content and calls the isolation a hobby.
A pronoun of respectful distance became the label for the most devoted audience on earth. What does the distance explain?