Otaku culture is one of the culture in Japan that is large enough to create a market for themselves. The word Otaku could be use to describe a Mania or someone who is having an obsession with something in particular. But it is more common to be use to referring the group that love Anime,Comic and Video game as a whole
What make this sub-culture interesting to the producer is the power to buy of the Otaku group is very high, they would buy things like a limited edition of the game or a whole set of figure and toy of the character they like just to be “hardcore” and show their love to the series. So even if your series of Anime finish or Your video game already release, you could still make the money off the related product since Otaku will still buy them. Even 10 Years old Anime like Evangelion is still alive and making money to the company (to the point that they’re remaking the series) because their product still sell off due to the Otaku sub-culture
They are also creating a new market for Japan by forcing back the things these Otaku love (usually something “cute” like a cat ears, or girls wearing certain type of clothes) back into the real world, the example we can see are the maid cafe.
Although the Otaku culture aren’t as strong in the US as in Japan, but they are gaining more popularity due to to import of Japan culture and the exchange culture on the internet.
So I think it is also a good idea to consider these type of customer if you’re going to do the business, since these guys would be the most loyal customer to the thing they like.