actually that's more like a weeaboo.
an otaku is someone who shuts out all other life forms and just lives in their house, reading manga, watching anime and living off food their mothers buy from the market.
an otaku does sound like a hikkikomori, but a hikkikomori is someone who doesn't go to school and spends time in their room all day.
and a weeaboo is someone obsessed with japanese culture and acts as though they are japanese or an anime character, although they are far from it, being of non-asian descent.