I suspect the cake may have been Red Velvet or German chocolate, Red Velvet being most likely because it was unknown to Nagto while German chocolate was both unknown to Nagano and is not the expected color of chocolate.
Ok... In this kancolle verse it's probably Iowa, but in our reality the responsibility for bringing German chocolate to Okinawa was aparently the army field kitchens and chow halls that made it and also trained some of the POWs and others who worked as cooks assistants during and after the occupation of Okinawa.
Boisterous as ever, aren't you.There's some rotten beans in the fridge!That had a weird colour to it.NAGATO!Now, now, don't say that. Just try a little bite.You didn't have any of the cake that I made either, didn't you, Nagato!Want to try it?This is that rumoured...BIG TROUBLE!!It's good for your body, see.That would be nattou.And this has a weird smell to it!Aaaand closing.
