Anecdotal evidence suggests that neither Mirror's Edge nor Mercenaries 2 took off in Japan. This picture shows stacks of new copies of both games on sale for ¥1,980 ($21). Mirror's Edge was released on December 11 in Japan, and Mercenaries 2 followed one week later. Both the Xbox 360 and PlayStation 3 versions are marked down, so the blame for poor sales doesn't fall solely on 360's lowly reputation in Japan.
Japan has no rental services, so people tend to buy games, complete them immediately, and then sell them back to stores asap, before the prices are slashed, leading to a precipitous drop in used prices of popular games. Even that isn't the case here -- these games are new, and retailer Sofmap's website shows used copies of Mirror's Edge at ¥4,780 for PS3 and 360, while new copies are marked down to a mere ¥1,980.
Would Mirror's Edge have benefited from a lead character redesigned for Asian audiences? Maybe, if that redesign had also encompassed not making the game a first-person shooter.