Twitter could be about to partner with one of Japan’s largest social networks, Mixi, after the duo revealed plans to hold a joint press conference next week, according to Japanese tech blog Asiajin.

A link-up between both services seems the most likely outcome, and Asiajin speculates that Mixi may replace Mixi-voice, the Twitter-like service that runs across its service, by integrating the microblogging site.

The partnership is likely to benefit both parties. Mixi is leaning on Twitter’s huge popularity in Japan to boost its user base of 22.39 million (as of December 2010), while Twitter could enjoy increased visibility through the link-up with one of Japan’s first popular social sites. Mixi competes for attention with three other local networks — including mobile social gaming platforms GREE and DeNA — but its link-up with Twitter comes as Facebook’s Japanese presence continues to grow.

Membership of the world’s largest social network in the country increased by more than 18 percent over the last three months, during which time it added 816,000 users, according to Facebook analytics specialist Socialbakers.

Japan is one of Twitter’s strongest markets — Japanese is its second most used language — and the microblogging service was the first overseas social network to make a significant impact in the country. Twitter co-founder Jack Dorsey recently revealed his surprise at the speed at which Twitter became popular, to the point that Japan’s dedicated Tamagotchi owners used it to feed their virtual pets.

Japanese Twitter users broke the record for the most tweets sent in a minute during last year’s football World Cup. Although that record has since been surpassed, when news of popstar Beyonce’s pregnancy broke, it serves as a further proof point of its popularity in the East Asia country.