Just before the New Year holiday in Japan, ads for a smartphone game called Granblue Fantasy began appearing on television and in magazines.

Granblue was already huge in Japan with more than 7 million people downloading it to fly giant airships and battle an evil empire with swords and magic. Cygames Inc., the company that makes the game, also told people about a new promotion: For a limited time, it would be easier to win a few characters, including one named Anchira.

Anchira is a rarely-seen, much-sought-after ally: blonde, scantily-clad, big-eyed. She's the kind of partner that can mean the difference between victory and defeat because of special healing powers. Players can win access to her with mysterious crystals that cost ¥300 apiece and then cracking them open to find out what is inside. Sometimes they contain valuable characters like Anchira; other times they hold weapons or armor. Under normal circumstances, there is a 3 percent chance of locating rare characters like Anchira, but for the week Cygames was running its promotion, the chances would double.