"Inu" (犬,"Inu"?) is Japanese for "dog", and jackals are in the same family as dogs.
In the 4Kids dub, this fruit is called the Mutt-Mutt Fruit: Jackal Strike.
In the Funimation dub, this fruit is called the Dog-Dog Fruit, Model: Jackal.
In the Viz Manga, this fruit is called the Mutt-Mutt Fruit: Jackal Model.
Strengths and Weaknesses
This fruit enables the eater to become a large, black jackal at will, granting an increase in physical strength, speed, and senses. Being a predatory canine, Chaka is better suited for physical combat than normal Zoans.
Aside from the standard Devil Fruit weakness, this fruit does not seem to have any specific weaknesses.
As seen by Chaka, this Devil Fruit increases both speed and power, allowing Chaka to jump onto the roof of Arabasta's castle, where Crocodile was sitting. Chaka has used this based on his emotions, turning into a Jackal when Crocodile enraged him, combining his animal strength with swordsmanship. Chaka has only shown a single attack.
Narikiba (鳴牙,Narikiba?, literally meaning "Howling Fang"): After transforming into his full jackal form, Chaka draws his sword, puts it into his mouth, and dashes towards his opponent swiping them with the blade. This attack was ineffective against Crocodile, who simply changed his body into sand to allow the strike to bypass him.
Translation and Dub Issues
Due to the fruit sharing a similar name to the Inu Inu no Mi, Model: Dachshund, the fruit was also renamed the Mutt-Mutt Fruit in the 4Kids dub. However, in order to differentiate it from the previous fruit, the words "Jackal Strike" were added to the name, although this may be an attack name in the dub. This type of naming convention has only been used for this fruit. Other Zoan-type fruits with different models, renamed in the 4Kids dub, do not share this style in order to differentiate one another.
This fruit represents the jackal, one of the two guardian spirits of Arabasta, along with Pell the Falcon. Both of them are based on the Egyptian deities Anubis and Horus, respectively.