Japanese mobile phone operator Docomo announced today it has completed its investment in Baidu Yi Xin Network Technology, its joint venture with Chinese search engine Baidu.

Originally spotted by TechCrunch, Docomo’s $22.5 million investment gives it a 20 percent ownership stake in the new mobile content distribution platform. According to today’s press release, the first Baidu Yi Xin games and services will begin roll out in August, and will be provided by existing Docomo partner DeNA.

Today’s announcement appears to be another extension of the partnership Docomo and DeNA set up last spring, when the two companies formed a strategic business alliance to promote the DeNA’s Mobage platform.

Originally the deal saw Mobage games and content directly linked to Docomo’s i-mode feature phone web portal, and a dedicated Mobage app pre-installed in certain Docomo smartphones. In November the two companies extended their alliance to Europe by including Docomo subsidiary net mobile AG in the deal, giving DeNA access to Docomo customers in Germany, Austria, Switzerland, the U.K. and Australia.

For DeNA, the deal gives it yet another in-road to the rapidly growing Chinese mobile market. The company has been snapping up strategic partnerships left and right in the country to make sure the Mobage platform reaches Chinese consumers no matter what network they’re on or what manufacturer they’re with.

DeNA has already struck a deal with phone manufacturer Huawei to have a Mobage app pre-installed on its phones and to have its game featured in the company’s HiSpace app store. It also has its own joint venture with NetDragon to localize and distribute its games. It has agreements with Chinese social networks Kaixin001 and Weibo that allow those platform’s users to log into DeNA with their existing accounts, and a deal with Renren that showcases Mobage games in a dedicated section of Renren’s mobile app.

Today’s announcement also supplements an existing deal DeNA struck with Baidu Yi Xin majority owner Baidu in February to have Mobage games show up in a dedicated section of the company’s Baidu Yi Android app store. Finally, DeNA has also signed deals with all three major Chinese mobile carriers to offer direct carrier billing to their customers and offer Mobage games in their app stores.