Azur Lane is a side-scrolling shoot 'em up video game created by Chinese developers Shanghai Manjuu and Xiamen Yongshi, released in 2017 for the iOS and Android operating systems. Set in an alternate timeline of World War II, players engage in side-scrolling shooter gameplay, using female moe anthropomorphic characters based on warships from the war's major participants. Other gameplay elements, like customizing a home and marrying in-game characters, are also present. First launched in China in May and in Japan in September 2017, Azur Lane has become very popular, especially in Japan where the player count reached five million within four months after its release. Players have voted the game among the top five on Google Play's Best Game of 2017 list for the region. Critics have attributed the game's popularity to its original and well-designed gameplay system.

Azur Lane is set in an alternate World War II timeline where Earth's oceans are invaded by a mysterious alien force known as the Sirens. These beings possess advanced technology far beyond humanity's capabilities, causing nations to lose over 90% of their maritime control. In response, four major naval powers—the Eagle Union (U. S. ), Royal Navy (UK), Iron Blood (Germany), and Sakura Empire (Japan)—form the Azur Lane alliance. They use Wisdom Cubes to create shipgirls (Kansen), humanoid embodiments of warships, to fight back. Initially successful, the alliance fractures when the Iron Blood and Sakura Empire defect to form the Crimson Axis (Red Axis). They adopt Siren technology to enhance their power, believing it is the only way to ensure humanity's survival. This ideological split reignites global conflict.