In winter, shellfish head in the direction of the dirt and become a luxury. Luxuries are things that are hard to get, which is why rich people like them so much. It shows they have the money and means to get things other people can't. So when these shellfish try to bury themselves deep, deep in the dirt in winter, they become the biggest luxury of them all.
You have your eyes on one of these luxury shellfish, and you're digging down into the cold dirt, when your fingers wrap around something hard and... long? You struggle to pull it out, but once you do, you realize you're holding a rare German saber: the zeiber (ぜい)!