Which of the following is not a specialty style of sake?

The choice identified as the correct answer is indeed the one that does not represent a specialty style of sake. Nigori, sparkling, and koshu are recognized specialty styles that have unique characteristics and methods of production.

Nigori is a cloudy sake made by partially filtering the rice, which gives it a characteristic milky appearance and often a sweeter, richer flavor profile. Sparkling sake is produced using methods that introduce carbonation, making it effervescent and often appealing for its refreshing qualities. Koshu refers to aged sake, which has been matured for a period of time, developing complex flavors and aromas that are not typical in younger sakes.

In contrast, the term "fruity" does not designate a specific style of sake but rather describes a potential flavor profile that can be found in many types of sake. Sake can exhibit a range of flavors and aromas influenced by various factors, including the rice used, the brewing process, and the water quality, but "fruity" itself is not an established category or style like the others listed.