Looking over Nutaku's Facebook page, those serial numbers you guys are talking about are probably tied to the Armor Blitz contest they're doing. One person from among the people who went to Nutaku's Anime Expo booth will get 10,000 gold and the ability to design a character for the game.

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Unless the serial number was explicitly for Kamihime when you got it, in which case you'd probably have to wait until after convention for an official announcement about what it's going to be used for, I guess.