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When Casey, a security officer in his early 30s from San Jose, California, first started playing the Japanese mobile game Puzzles & Dragons, he was obsessed. "I would play constantly, everyday," he says. "Even on my breaks at work, I would play non-stop." During his first month, he estimates that he spent about $600 in the game, mainly to obtain special characters (many Japanese games use a "Gacha" mechanism where users can spin to win prizes). He says he has friends who he knows have spent thousands of dollars on Puzzles & Dragons.

Although Casey lives in California, not Japan, his playing habits resembled those of a typical Japanese gamer: super high engagement and a willingness to shell out real money. Japan is the top market for mobile game revenue and its spoils have surpassed mobile gaming revenue in the United States for the third year in a row, according to data from App Annie, despite the fact that the U.S. has three times as many smartphone users. Japan ranks highest in terms of average number of sessions in games per app user, and Japanese mobile app users use gaming apps twice as frequently as users in the US.

A balanced split between iOS and Android

Of the 12 public companies that have disclosed that they are generating 25% or more of their revenue through Google parent company Alphabet, the seven most reliant are all Japanese app developers, according to data from FactSet. These companies make money through the Google Play Store.

Companies most dependent on Alphabet Company Industry Alphabet reliance Market Cap Country Ignis App developer 48% $24.8 bln Japan Colopl App developer 40.70% $156 bln Japan Gungho App developer 35.70% $300.9 bln Japan Gumi App developer 35% $32.1 bln Japan KLab App developer 33.80% $70.2 bln Japan Voltage App developer 33.40% $5.5 bln Japan Cave Interactive App developer 30.10% $6.65 bln USA Inuvo Ad-tech 29.70% $22.3 bln USA Zynga App developer 29% $3.5 bln USA Glu Mobile App developer 27.60% $505.6 mln USA IAC internet and media 26% $10.2 bln USA Ateam internet and media 25.95% $54 bln Japan

Gungho, the company that created Puzzles & Dragons, makes 35.7% of its revenue from Google Play and 54.1% from Apple's App Store, according to FactSet. The company most reliant on Google Play, Ignis, sourced 48% of its revenue through Play and 38.1% of its revenue through the App Store. That highlights what's particularly interesting about Japan: The Japanese mobile game market leans more heavily toward Google's Android platform than other markets. Consider Zynga, the American app company with the highest disclosed percentage of its revenue coming from Alphabet: The breakdown is 29% Google Play Store, 46% Apple App Store. That's in line with the conventional wisdom that iPhone users are generally wealthier than Android users and tend to spend significantly more on apps overall. But Japan's mobile gaming market bucks that trend. In many other parts of the world, Android phone owners will use a forked version of the Android operating system that has a different app store. But the Google Play Store has a wide download base in Japan, according to Lexi Sydow, market insights manager at App Annie.