Densuke watermelons are grown exclusively on the island of Hokkaido in northern Japan. Production is centralized in the town of Tohma – where the island's specific climate and mineral-rich volcanic soil make cultivating the fruit possible. A variety of Black Diamond watermelon, the Densuke was introduced in 1981 when Hokkaido farmers began switching to crops outside of traditional rice paddies. The Densuke name was trademarked in 1989, and only watermelons grown in the region that pass a rigorous inspection process can be certified as genuine. They are labor-intensive and require a large amount of acreage, water, and attention to thrive, and for those reasons, only a limited supply is available each growing season. 

The Densuke's black watermelon rind encloses red, juicy flesh, described as firm and crunchy, with the delicious taste markedly sweeter due to its higher sugar content. Fruit is held in high regard in Japanese society, and the Densuke is considered the king of watermelons, so they are treated accordingly like royalty — from planting to picking to packing. Resembling engorged bowling balls, the melons are repeatedly turned by hand while still on the vine, to avoid uneven growth, discoloration, bruising, or soft spots. Once harvested, each melon is polished to a glistening black sheen, then assessed for quality and appearance before receiving an inspection sticker as a certificate of origin and authenticity, and then each is packaged in distinctive gift boxes.