Welcome to the NHK (TV)

The poster in Satou's room is a parody of the Vincent Gallo film Buffalo '66.

On the flyer near the end of Episode 14 and in following two episodes, the name of the Massively Multiplayer Online game is called "Ultimate Fantasy". This game is a reference to Square Enix's Final Fantasy XI.

The real-life television company NHK (Nippon Hōsō Kyōkai), which is the source of the acronym that is parodied by the series, really does provide a support website for real-life hikikomori[2]. It is not known if the existence of this website was related to the use of their acronym as a parody related to hikikomori. In the manga, a concrete link between the television company NHK and Satō's Nihon Hikikomori Kyokai is implied; in the anime, although the conspiracy is still named NHK, no such correspondence is drawn and it appears that the NHK does not even exist as a television company in the anime's version of Japan. (In the anime, Misaki has never heard of the acronym when Satō says it to her.) This may have been due to the fact that the anime was broadcast on TV on channels operated by other Japanese broadcasting companies, thus implying that it related to the real TV company could have been interpreted as slander against a competitor.

The gray pullover Tatsuhiro wears by the end of episode 19 spells "ХУЙ" on it, which is a prominent obscene word in Russian meaning "male genitalia". Wearing such T-shirt may mean that the wearer is fed up with the world and wants to challenge it with an obvious obscenity.

The brand for Satou's desktop is Pujitsu instead of Fujitsu. His refrigerator is of Naier instead of Haier. His cigarette is Walboro instead of Malboro. Meanwhile, the OS used by the characters is Mindows XX instead of Windows XP.

ADV Films paid $240,000 to license the series in 2007.

In episode 4, there's a promotional poster behind where Saito and Yamazaki are sitting. That poster is from Gonzo's upcoming OVA series Strike Witches.

In episode 5 at around 3:11, you can see the name GONZO on one of the buildings, which is the name of the studio that produced the anime

In episode 6 at around 15:27, there is a poster of Otome Asakura and (a slightly more shrouded) Yume Asakura from the gal-game "Da Capo II" in the background of the classroom.

In episode 9 and again in episode 12 the opening theme to the British sitcom Black Books is heard.

In episode 12, you can see the kid at the island playing the Lemmings made by DMA Design in the DS screen.

in episode 21, you can see parody posters of X-Men 3 in the subway, but instead they say "NHK Men"

In episode 21, around 15:41, Sato is making signs with his hands like they do in Naruto when they use ninjutsu.