Eel pie, Japan always was one for fish flavored snacks, I guess in this case it's a confectionery. Reading the company's story behind the snack it seems this product was associated with the catch-phrase "a night-time snack", hence the premise of the image. The company contends the idea was for families to enjoy it and spend a nice time together in the evening, but apparently given the reputation for unagi to "restore energy or virility", they acknowledge customers have also attributed other meanings to the snack's catch phrase. Not sure if that implies any sort of deeper allusion or implication to the image here.