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Dragon Quest IX: Sentinels of the Starry Skies is a 2009 role-playing video game developed by Level-5 for the Nintendo DS. Dragon Quest IX introduced local multiplayer functionality to the series, as well as limited compatibility with Nintendo Wi-Fi Connection. It was also the first to be initially released for a handheld game console, and the first to feature spawning of enemies, rather than random encounters. The game retains many of the series' traditional role-playing elements, such as turn-based combat and a level system based on gaining experience points. The game was designed to be the most difficult one in the series, and was released in Japan by Square Enix in July 2009, and worldwide by Nintendo in July 2010.

Dragon Quest IX achieved record-breaking sales within Japan, and has set a Guinness World Record for its anonymous communication mode. Critically, the game has been well-received both inside and outside Japan.