Juku comes from Jukusuru (熟する) which means to mature in Japanese.
Its English name "Ripe" is another term for maturing.
Strengths and Weaknesses
By simply touching an inanimate object, the user will cause it to rapidly age and decay. Using it on the ground will cause it to become a sinkhole, allowing the user to potentially avoid attacks by sinking into the ground. The fruit can also help the user get past physical obstacles by weakening them through aging, causing them to collapse or be easily broken through.
The rate of decay will continue to progress once triggered, thus leading to potential problems after the initial purpose, such as a sinkhole becoming deeper until it reaches to the ocean. Other than that, the fruit has no known weaknesses aside from the standard Devil Fruit weaknesses.
Shinobu, like other Devil Fruit users from Wano Country, refers to her powers as a "jutsu". She was seen using this power to create a hole in the ground to escape Kaido's devastating Bolo Breath.
Sexy Ninpo: Kare-San-Sui (熟々忍法 枯散衰,Sekushī Ninpō: Kare San Sui?, literally meaning "Mature-Mature Ninja Art: Wither-Scatter-Decline): Shinobu touches the ceiling in which she hides and makes it collapse in order to escape. In the VIZ translation, this is called Sexy Ninpo: Rot Garden. The technique's name may be a pun on karesansui (枯山水,karesansui?), "dry landscape", a term for the Japanese rock garden.
This fruit is similar to the unnamed fruit eaten by Jewelry Bonney as both fruits focus on aging, with Bonney's fruit affecting living beings. Unlike this fruit, Bonney's fruit can also make beings younger.