Haganai (TV)

In ep 2, they refer to a PSP, "Playstation Portable", as a "Playingstates Portable."

In ep 2, when Yozora is placing the bomb next to sena, while walking away she is humming a empire Star Wars theme

In ep 2, during the second attempt at playing games, the game console they use is a "Playingstates III," a clear spin off of the actual PS3 (Playstation 3)

In Episode 2, the second girl with glasses in the dating sim game is named Nagata Yukiko. The name resembles Nagato Yuki from The Melancholy of Haruhi Suzumiya. Nagato Yuki also loves the library which is where the character meets Nagata Yukiko.

In Episode 2, Yozora is not humming the Star Wars theme after planting the bomb next to Sena. She is actually humming Richard Wagner's "The Ride of the Valkyries" from the 1870 opera Die Walküre. This music is famously known for its use in the 1979 film "Apocalypse Now" during the scene where US Army helicopters are indiscriminately strafing and blowing up a Vietnamese Việt Cộng village and its surrounding real estate.

In Episode 2 at 3:00, the game on the PSP has a title screen called Monster Portable III. This is a reference to the Monster Hunter franchise.

in Episode 3, the background around 2:50 you can see 2 characters strongly resembling Luke and Cecily from the Sacred Blacksmith.

In episode 4, two mechas featured are obvious parodies of Gundam and the EVA unit 2 from Neon Genesis Evangelion

In episode 5, in the game world Maria is dressed up like Index from To Aru Majutsu no Index. Maria's voice actress Yuka Iguchi also performs the voice for Index.

During 8.25-8.30 in episode 5, Sena is referring to Luke Ainsworth of "The Sacred Blacksmith" series.

In episode 5 around 17:20 Sena says to Kodaka that his little sister can't be this cute, using a phrase which is almost identical to the title of the series Ore no Imōto ga Konnani Kawaii Wake ga Nai. In that series the charecter Ruri Gokou (Kuroneko) shares many characteristics with Kobato Hasegawa and both are voiced by Hanazawa Kana.

In episode 5, Rika's outfit and hairstyle are tribute to Yoko from Gurren Lagann, which is incedently voiced by Yozora Mikazuki's voce actress.

In episode 6, the blue silhouette at the chapter title, is doing the dance-like movements of Cygnus Hyouga from Saint Seiya.

In episode 7, around 7:05, Sena is going on about a game she played for hours. It is a parody of one of the KEY's creation, AIR (AIR TV and Game). The name of the character Mikane is an alternative name for Misuzu.

In Episode 7 at 18:00, there is a guy looking at a magazine called Play Guy. This is most likely a reference to Playboy Magazines.

In episode 8, around 8:30 at the time Kodaka brought his younger sister Kobato to the club room, Rika suddenly asked Kobato "What kind of panties are you wearing?" is the reference from another anime called K-On! when Ritsu said the same words to make fun on Mio in season two episode fourteen.

In Episode 8 before the OP, the AC unit stopped working with the brand, Megasonic. This is a play of Panasonic.

In episode 11, when Rika is talking about the time she tried to attend Comiket, four characters from Ore no Imouto ga Konnani Kawaii Wake ga Nai (Oreimo), Saori, Ruri, Kirino, and Kyousuke, can be seen walking on the right at about 4:31.

In episode 11,the game console Rika won in the Matsuri is a Microsoft XBOX 360 Premium.

In Episode 12, Rika had Yozora dress up in a cosplay outfit. This outfit is extremely similar, if not the same, to the outfit that Lelouch Vi Britannia from Code Geass wore when he became emperor. Lelouch also had short black hair and purple eyes, just like Yozora. Later in the anime, Rika brings out a white cape which is also what Lelouch wore. The director of Haganai, Hisashi Saito, was also staff to the second season of Code Geass; the reference to Lelouch could be Saito's homage to Code Geass.