The board refused classification of the novels on July 23, and stated regarding the refusal for volumes 1 and 2:
Pubs 1(b): The publication is classified RC in accordance with the National Classification Code, Publications Table, 1. (b) as publications that "describe or depict in a way that is likely to cause offence to a reasonable adult, a person who is, or appears to be, a child under 18 (whether the person is engaged in sexual activity or not)."
In addition, for volume 9, the board gave this statement regarding the refusal:
Pubs 1(a)&(b): The publication is classified RC in accordance with the National Classification Code, Publications Table, 1. (a) as publications that "describe, depict, express or otherwise deal with matters of sex, drug misuse or addiction, crime, cruelty, violence or revolting or abhorrent phenomena in such a way that they offend against the standards of morality, decency and propriety generally accepted by reasonable adults to the extent that they should not be classified," and (b) "describe or depict in a way that is likely to cause offence to a reasonable adult, a person who is, or appears to be, a child under 18 (whether the person is engaged in sexual activity or not)."
According to the Australian Classification Board's website, titles classified as refused "cannot be sold, hired, advertised or legally imported in Australia. RC-classified material contains content that is very high in impact and falls outside generally-accepted community standards."
The board had restricted the No Game, No Life television anime series as MA 15+ for strong sexual themes on August 13, 2015. The series is "legally restricted to people over the age of 15," but is otherwise available for sale. The board also restricted the No Game, No Life Zero anime film as M for fantasy themes and animated violence on November 10, 2017. While the board states that the film is "not recommended for children under the age of 15," there are no legal restrictions against selling or viewing the film.
The story of Kamiya's No Game, No Life light novel series centers around Sora and Shiro, a brother and sister whose reputations as brilliant NEET (Not in Education, Employment, or Training) hikikomori (shut-in) gamers have spawned urban legends all over the Internet. These two gamers even consider the real world as just another "crappy game." One day, they are summoned by a boy named "God" to an alternate world. There, God has prohibited war and declared this to be a world where "everything is decided by games" — even national borders. Humanity has been driven back into one remaining city by the other races. Will Sora and Shiro, the good-for-nothing brother and sister, become the "Saviors of Humanity" on this alternate world? "Well, let's start playing."
Kamiya launched the light novel series in 2012 with his own art after illustrating another light novel series that spawned an anime, A Dark Rabbit Has Seven Lives (Itsuka Tenma no Kurousagi). Hiiragi launched the manga adaptation in Media Factory's Comic Alive magazine in 2013.
The light novel series inspired a 12-episode anime series in 2014. Crunchyroll streamed the series as it aired, and Sentai Filmworks released the series on home video in July 2015. The light novel series also inspired an anime film.
Thanks to CatSword for the news tip.
Update: The political party Centre Alliance applied for these novel volumes' classification. In February, Stirling Griff from the Centre Alliance called for a review of all anime and manga currently accessible in Australia, expressing concerns about media depicting "child exploitation." The Sydney branch of the Books Kinokuniya store chain removed seven manga titles, including No Game, No Life, from its shelves following a written complaint by South Australian legislator Connie Bonaros. Bonaros belongs to the SA-Best party, the Centre Alliance's affiliate party for South Australian state elections. (Bonaros was Griff's former chief of staff.) Thanks, Greboruri.