I forget if it was ever explained in any tl notes on the old chapters, but Engi is based on the Japanese myth that if your first dream of the new year involves an Mt. Fuji, a hawk, and an eggplant, you'll have good luck that year. "nasu" means eggplant, hence Sannasubi and her nickname "eggplant lady". Also why she suggests Mt. Fuji as the "largest living thing in the world", and has triangular pupils. Then her hair looks like (hawk) wings.
apologies if this is common knowledge.