The protagonist of Max Brooks’s new fantasy novel doesn’t have a name, a gender or even normal human appendages. Instead of hands, the narrator has clumsy, flesh-toned cubes, just one more weird feature of the strange and unsettling world where the story unfolds, where everything — the sun, clouds, cows, mushrooms, watermelons — is composed of squares.

For the uninitiated, the setting may seem bizarre and disorienting, but Mr. Brooks isn’t writing for novices or lay readers. He’s writing for a very particular tribe: die-hard devotees of the video game Minecraft.

“Minecraft: The Island,” which was released this month by the science fiction and fantasy publisher Del Rey, represents an unusual experiment in multiplatform brand extension. It marks the first officially sanctioned novel commissioned by Mojang, the Swedish game studio behind Minecraft, as the company seeks new ways to capitalize on the game’s enormous popularity. (To eliminate any doubt about the company’s consent, Mojang’s name and logo appear twice on the book’s cover, which bears the bland endorsement, “Mojang Official Product.”)

Unlike most video and computer games, Minecraft doesn’t have clear-cut objectives or levels to ascend. Instead, it’s more like an elaborate digital Lego set that allows players to build whatever they like, designing their own castles, skyscrapers, underground bunkers and booby traps.

The open-ended nature of the game is a big part of its appeal. Since its release in 2011, Minecraft has sold more than 122 million copies and now has 55 million active monthly users. The game’s user base exploded so rapidly that in 2014, Microsoft bought the company for $2.5 billion.

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As product spinoffs go, a series of novels seems like a natural step for Mojang, which already has a wildly successful publishing line of gaming manuals. (A feature film is also in the works, at Warner Bros.) Since 2013, the children’s publisher Scholastic has published 10 Minecraft titles, which have 25 million copies in print. On Amazon, there are thousands more unofficial titles that fans have self-published, including entire novels set inside the game.

“We had been thinking about fiction for a long time but wanted to make sure that it didn’t take away from people’s experience of the game, because everyone plays in a different way,” said Lydia Winters, Mojang’s brand director.

But commissioning a brand-approved Minecraft novel posed unique creative and commercial challenges. How do you create a story with a beginning, a middle and an end out of an open-ended game? And would gamers bother to pick up a nearly 300-page novel about Minecraft, when they could be spending their free time playing it?

Mr. Brooks — a cheerful, enthusiastic paranoiac who is obsessed with survival strategies, zombies, apocalyptic scenarios and plagues — wrote the story as a first-person, Robinson Crusoe-esque narrative, featuring an initially hapless character who is stranded on a strange island and has to build shelter, find food and fight off zombies and giant spiders, all features that exist in the game.

When Mojang approached him to write a Minecraft novel in fall 2015, Mr. Brooks already had a track record as a best-selling author. The son of the actor Mel Brooks and the actress Anne Bancroft, Max Brooks turned to fiction after a brief and unremarkable career in comedy writing, which included a stint as a writer for “Saturday Night Live.”

After he was fired from the show, he started writing chillingly realistic zombie fiction and found his calling. Two of his previous books, “World War Z” and “The Zombie Survival Guide,” have collectively sold more than 3.5 million copies, and “World War Z,” a faux oral history about the aftermath of a zombie apocalypse, was adapted into a feature film starring Brad Pitt.

Other successful authors might have brushed off an invitation to write a video game tie-in novel, an unabashedly commercial genre that some say amounts to little more than elaborate product placement. But Mr. Brooks happens to be an avid Minecraft player and jumped at the opportunity. He was determined to write a story that mirrored the experience of playing the game. He developed a plot that conformed to the Minecraft universe so closely that someone reading the book could recreate the narrative within the game and play along.

“I war-gamed out everything,” Mr. Brooks said in a recent interview from his home in Los Angeles. “My biggest fear was that somebody tries to play out my book and finds out it won’t work.”

In the process, he may have also created a strange new entertainment category, one that hovers somewhere between fan fiction, role-playing games and literature — a novel set in a game, that can itself be played within the game.

Like reverse adaptations of movies and TV shows (see, for example, novels based on “Buffy the Vampire Slayer” and “CSI”), novels based on gaming franchises have long been a lucrative niche within the publishing industry.

Publishers have been releasing novels based on popular video games for decades, hoping to capture a slice of the medium’s huge fan base. Gallery Books, an imprint of Simon & Schuster, has published fictional series based on games like Halo, Doom and World of Warcraft, and has millions of copies of its video game tie-in novels in circulation. Other publishers have built fictional franchises based on games like Gears of War, Starcraft, BioShock and Tomb Raider.

“Especially with teenage boys, it’s one of the only ways we can get them to read,” said Keith Clayton, the associate publisher at Del Rey.

To market its Minecraft novel, Del Rey has been assiduously courting players. The project was announced with fanfare last year at Minecon in Anaheim, Calif., a fan convention that drew 14,000 people. Del Rey is promoting the novel within the game’s platform, with a digital replica of the island Mr. Brooks created, which players can explore. They are also advertising on YouTube, where videos of people playing the game have become a popular subgenre.

Mr. Brooks, 45, began playing Minecraft five years ago, after a family friend showed him how the game worked. He began playing regularly with his son, who is now 12, and was immediately sucked in by the creative possibilities of the game.

When Mojang asked if he would be interested in writing a Minecraft novel, Mr. Brooks was so enthusiastic that he wrote a full draft before his contract was even completed. For the most part, Mojang gave him freedom to write the story however he wanted. The company’s only instructions had to do with the protagonist’s physical appearance.

“They were very hands off when it came to the story, but very hands on when it came to inclusiveness,” he said.

Mojang wanted to make sure that any Minecraft player could pick up the novel and imagine himself or herself in it. The company even commissioned two different versions of the audiobook, one by a female narrator, Samira Wiley, and another by a man, the actor Jack Black, so that listeners can choose a narrator of either gender.

Keeping the character’s identity ambiguous wasn’t too hard: Because the hero is stranded alone on an island, with only animals and other ghoulish creatures to talk to, Mr. Brooks was able to avoid using gendered pronouns.

Mr. Brooks concedes that the novel, which is geared toward 8- to 12-year-olds, might not hold much appeal for those who are unfamiliar with the game.

The plot was created for players, and perhaps parents and grandparents who want to understand the game’s appeal, Mr. Brooks said.

Above all, though, Mr. Brooks wrote it to satisfy his own creative impulses.

“Honestly, at the end of it all, I wrote it for me,” he said. “I’m a fan first.”