Although Mosdo, the partnership between Japanese chains Mos Burger and Mister Donut, has been around since last year, they never truly married their main offerings to make a doughnut burger. Until now. (Feel free to correct me if I'm wrong as my Japanese skills are almost nonexistent.)
This teaser implies that the debut date for the doughnut burger is May 12. Japanese pop star Nozomi Tsuji received a doughnut burger tasting invitation (English translation) for this Wednesday, so maybe she'll give a report about it.
Related: MOS Burger!