Inu Inu no Mi, Model: Okuchi no Makami

The Inu Inu no Mi, Model: Okuchi no Makami is a Mythical Zoan-type Devil Fruit that allows the user to transform into a wolf deity. It was eaten by Yamato.

As noted by Kaido, said wolf is the "Guardian Deity of Wano Country" (ワノ国の守り神), making this Zoan particularly valuable. Its power was first hinted at during Yamato's confrontation with Sasaki when Yamato briefly flashed their fangs, before its power was properly introduced in Yamato's later fight with Kaido on the Skull Dome's roof.

Etymology

 * Inu (犬) is Japanese for "dog".
 * The "Ōkuchi-no-Magami" or "Ōguchi-no-Makami" (大口真神) is the deification of the extinct Japanese gray wolf, once worshipped in Japan as a guardian deity of humans.

Strengths and Weaknesses
This fruit's power, as shown by Yamato, allows the user to transform into a hybrid and full version of the Okuchi no Makami, a legendary wolf that, according to Kaido, is the guardian deity of Wano. While transformed, the user's hair becomes longer and more untamed, with a ribbon-like trail of flames encircling their shoulders.

The transformation not only boosts the user's physical abilities to a notable degree, as a carnivorous Zoan, it presumably bestows a heightened predatory instinct, on top of equipping the user with fangs and claws well-suited for combat. More specifically, the wolf form seems to come with a dramatic increase in physical strength, in Yamato's case enough to let them clash near-evenly with their father Kaido, an Emperor of the Sea, while the latter has assumed his extremely powerful human-dragon form.

Moreover, as with other fruits of the Mythical Zoan variety, this one blesses the user with at least one special ability: in particular, the user becomes able to expel powerful blasts of what looks like flames (or some similar substance) from the mouth, not unlike what Kaido's Mythical dragon Zoan allows him to do.

No weaknesses are currently known of this ability beside the standard ones for a Devil Fruit user.

Usage
Yamato utilizes this ability for battle. They have proved able, in their Human-Beast Form, to fight on nigh-even grounds against their father, Kaido, while the latter was in his half-dragon form, having Kaido commend their level of strength. In Yamato's hybrid form, they prefer to still wield their kanabo like they do in Human Form, enhancing their melee combat prowess.

Techniques
Namuji Hyoga: An attack where Yamato rears back their head, takes a deep breath, and then abruptly exhales forward a dense blast, apparently made of flames of some kind (or possibly even ice, judging by the name), at their target of choice. First seen used by Yamato in their Human-Beast Form against Kaido, atop the Skull Dome, the attack proved strong enough to clash against and counter Kaido's Bolo Breath (used by the latter in his own hybrid form). In the VIZ manga, the technique is called Namuji Glacier Fang.

History
Kaido claims to have had a difficult time acquiring this Devil Fruit and never intended for it to be eaten by Yamato. Regardless, at some point, the latter came across it and, not knowing the fruit's nature, ate it out of hunger, gaining its powers at the cost of losing the ability to swim, and thus giving Yamato even less hope of ever escaping from Onigashima on their own.

Trivia

 * This fruit is the second model of the Inu Inu no Mi series that is based on a wolf species, the first being Jabra's regular wolf Zoan. It is also the second (canon) Mythical variant of the dog Zoan, being introduced in the same story arc as the first one (that is based on another canine from Japanese folklore).
 * The Ōkuchi-no-Magami—or simply Makami/Magami (真神)—is the deification of the now-extinct Japanese wolf, which was traditionally worshipped as a sacred beast in Japan, like the Yamato Province (present-day Nara Prefecture). For centuries, the Makami had been thought of as a guardian deity that understood human language and protected humans from misfortune, fire and theft, their crops from despoilment by animals, et al. Once a rather popular folkloric figure, the Makami's worship fell into decline with the rapid depopulation of Japanese wolves following the Edo period, during Japan's Meiji era when systematic wolf hunting culled the species until it went extinct in the early 1900s. Today, the Makami is a relatively obscure deity, though it remains enshrined at various locations, like the nearly 2000-year-old Mitsumine Shrine in Chichibu-Tama-Kai National Park.
 * Yamato possessing this fruit's power may also reference a particular mythological tale from the 2nd century AD, about the legendary Japanese prince of the Yamato dynasty, Yamato Takeru (possibly Yamato's namesake). The story tells of a white wolf whom said prince encountered in a moment of despair, after having gone astray in the mountains. Said wolf guided the prince out the mountains' deep forests and thereby saved his life. In appreciation, the prince supposedly had many shrines constructed in dedication to the wolf god of the mountains, including the above-mentioned Mitsumine Shrine in Chichibu, Saitama (the supposed location of said mountains).
 * The trail of flames around Yamato's shoulders, forming a circle behind her head, resembles the floating, ribbon-like drapery that can be found with certain depictions of East Asian (such as Buddhist) deities, including on Japanese statuary, befitting the Ōkuchi-no-Magami's own status as a deity.