Tosogu sometimes have Nasu(bi) depicted on them. I began to wonder about the symbolism of Nasu 茄子 and how they came to be considered good luck in Japan.
Some casual reading dredged up the following. If anyone cares to add or subtract from this, please feel welcome to participate.
The first and most popular reference seems to be to the important New Year's first dream scenario, １富士２鷹３茄子 where if your very first dream is about Mt Fuji you will have a seriously propitious year ahead.
The order starts 1. Mt Fuji, 2. Taka (hawk) 3. Nasu... and goes on to... 4. A fan 5. Tobacco and 6. Zato.
So if you dream of eggplants, that is the third luckiest of dreams to have!
The reasons for their luck seem to be a little more obscure. They symbolized wealth and child-bearing. Could this be connected with the second character 茄子 being 子 child?
One reason common to both Nasu and Zato, (the bald figure seated on a cushion, like Biwa no Hoshi) is that both eggplants and Zato are hairless, 毛がなし (Ke. ga. nashi. = No hair). When spoken this sounds like 怪我なし (Kega. nashi. = no injuries). Japanese humour at its best, where baldness sends everyone into paroxysms of laughter, and the bald guy on stage is subjected to endless jokes and slapstick.
Finally they have tradionally been valued for their medicinal value.
So, to summarize, aubergines were traditionally virile, medicinal, and being bald, would keep you safe from injury. (?)