After finishing Gunbuster and Nadia, Gainax released a two-part OVA in 1991 called Otaku no Video. The anime's story is based on the rise of Gainax itself: a bunch of obsessed fanboys conquer the world of animation, and then the world at large! The main characters are Tanaka and Kubo, old high school classmates who haven't seen each other in years. Kubo is popular and successful, an all-star tennis player with a hot, cool girlfriend, whereas Tanaka and his buddies are otaku nerds to the core. Tanaka gradually "corrupts" Kubo by indocrinating him into the world of sci-fi geekdom, and Kubo gradually quits tennis, loses his girlfriend, and vows to become the greatest otaku of all, an Otaking!
Interspersed throughout are short, live action interviews in a mockumentary style that portray hardcore otaku of every stripe, military otaku, anime otaku, cel otaku, etc. These range from hilarious to damning portrayals, and one even has the camera crew running after a confused otaku in the street like some kind of public enemy :)
Otaku no Video is another Gainax classic: great story, likeable characters, and a tongue-in-cheek attitude toward the entire otaku phenomenon. It's loaded with anime references, but since the anime is itself about fandom, the references are fun and appropriate, rather than distracting (keep an eye out for nods to Lupin, Nadia, and plenty of anime I've never seen). The music is charming even when formulaic, and the opening theme, "Tatakae O