The Uo Uo no Mi, Model: Seiryu is a Mythical Zoan-type Devil Fruit that allows the user to transform into a hybrid and full version of an Azure Dragon at will. It was eaten by Kaidou during the God Valley Incident.
At some point after Kaidou had partaken of the fruit, he had a sample of his Lineage Factor extracted by Vegapunk, who used it to create an artificial Devil Fruit granting the same ability, though the result was deemed a failure; said fruit was eventually consumed by Kozuki Momonosuke, who since can become a pink dragon.
The fruit is spherical and slightly oblong in shape, somewhat resembling a pinecone. Its blue exterior gives the appearance of having overlapping scales: each "scale" has a small, dark-blue oval in the middle that bears a signature Devil Fruit spiral at the bottom, while the scales' outer portions are of a lighter-blue shade. On its top, the fruit possesses orange leaves and two identical, separate stems, with one being purple and the other a lighter pink shade.
This fruit enables the user to turn into a giant, serpentine, blue-scaled dragon—specifically a type of Eastern dragon (龍 Ryū?) called the "Azure Dragon"—and into a human-dragon hybrid. Apart from scales, acquired dragon features include horns (a second pair in Kaidou's case), sharp fangs, and limbs with clawed hands and feet. In his full Beast Form, Kaidou grows to rival a small town in size, making this the largest yet-seen Zoan transformation. His Human-Beast Form, while not as colossal, is still very large and, in shape, comes closer to his Human Form, with scales on his arms, outer torso, back, and legs as well as six horns on his head, claws on the hands and feet, and a long tail.
In addition to his standard Human-Beast Form, Kaidou has on several occasions showcased an alternate hybrid form. This form appears slightly bulkier and has different facial features: a full set of fangs, a larger nose, and eyebrows similar to his Beast form. These characteristics may give a possible indication of the Emperor drawing on more power from his Devil Fruit.
Strengths and Weaknesses
As with all Zoans, the user's transformation significantly boosts their physical abilities. The full dragon form's strength befits its size, as the user can severely damage structures like houses merely by brushing by them. When Kaidou flew around Okobore Town in a drunken stupor, it was believed that, if he continued wreaking havoc senselessly, not just the town but Kuri itself would get wiped out. The user's arms, while thinner compared to the rest of their dragon body, are still very strong, a single swipe of which can send large fish-men flying through stone structures with great force and rip apart houses with ease, even when drunk. In the anime, the full dragon form's power is further exemplified, with Kaidou seen causing intense, gusty shockwaves simply by moving through the air or being thrown around, as well as with a mere puff or burp. He was able to send Monkey D. Luffy flying with immense force using a tail swipe and easily overpowered Luffy's Haki-imbued use of Gear 3 with one of his dragon hands, as well as by thrusting his head forward. Two decades ago in his fight with Kozuki Oden, Kaidou in his Beast Form repeatedly clashed with the samurai on even terms, including matching the force of Oden's Togen Shirataki with his head, countering his blades with his claws and fangs, and even using one of his mustache tendrils to ensnare and toss Oden away.
The scales covering the user's dragon body are noted to be extremely durable. Blows of incredible power, including ones strengthened by regular Busoshoku Haki, have proven utterly ineffective at hurting Kaidou—e.g., when in full dragon form, he shrugged off a nonstop pummeling by Luffy's strongest Gear 3 attacks, without being scathed in the slightest. Nonetheless, as with Kaidou's extremely tough human skin, his dragon scales can be penetrated, and blood drawn from him, using attacks that bypass external defenses, like advanced-grade Busoshoku Haki.
Beside the transformation itself, the fruit bestows multiple supernatural abilities, the most out of any Mythical Zoan seen so far. The most prominent of these is the power to conjure Flame Clouds (焔雲 Homura-gumo?), with which the user can travel through the air by using them as footholds, effectively enabling flight; Kaidou's dragon arms tend to be continuously encircled by fiery rings, which may be said clouds helping him fly more effectively through the air. Also, the Flame Clouds can be used to lift other objects, including entire islands, into the air and move them, for extended periods even and while using their other powers simultaneously. Furthermore, there is no apparent need for the user to transform in order to manifest (or at least maintain) Flame Clouds.
In addition, the user can create and control various elements as a dragon, both in their full Beast and Human-Beast Form. The most commonly seen element used is fire, such as a concentrated scorching blast of fire that the user breathes out, which can travel many kilometers in the span of seconds and instantly decimate a large, earthen structure, as well as rapidly shooting fireballs in the anime. Aside from flames, the user can launch lightning bolts while roaring (Kaido is able to summon lightning bolts from the sky without transforming as seen in the anime) and cutting blades of wind while blowing, on top of stirring up strong, fast-rotating tornados. It is also shown that Kaido can summon large hails of ice in the video games.
The user's Human-Beast Form sees their draconic strength focused in significantly smaller frame, with this diminished size granting them a boost in agility and speed while seeming overall better adapted to close combat. The user also retains access to their elemental attacks, like their fire breath (though with a smaller range in accordance with their smaller body size, compared to their full dragon form).
Due to the massive amount of space the user takes up after entering their full Beast Form, their ability to move about in enclosed spaces is greatly hindered. Additionally, depending on how much care is given to their surroundings, the user's transformed body having a propensity for collateral damage may become a liability for allies. The user's massive body also leaves more openings, making them an easier target for attacks, especially multi-directional assault from more than one enemy.
While the user's dragon scales are immensely tough, the user remains vulnerable to attacks that, by their nature, can bypass external defenses. Usage of advanced, emitted Busoshoku Haki, in particular, can let opposing parties hurt the user's dragon form (even if used by enemies that are physically far weaker than the user), as can Haoshoku-infused attacks. Other examples of effective attacks reaching the target's insides are ones utilizing powerful soundwaves or the Ope Ope no Mi's "surgical" techniques.
Besides all these factors, the user is affected by the standard Devil Fruit weaknesses.
Kaidou uses this fruit's power frequently in combat. He typically starts out battles in his full dragon form and transforms back into a human upon getting more serious, his base form seeming more suited for intense and up-close, one-on-one combat. If his adversaries prove strong enough to handle both his human and full dragon forms, Kaidou will enter his Human-Beast Form—quite possibly the strongest of his three basic forms, it is generally used in all out fights against stronger and faster enemies that his two other forms have trouble dealing with.
When engaging foes in his full dragon form, Kaidou frequently hovers a considerable distance away from them, out of melee range, so as to assault them with destructive, long-ranged attacks of various elements, like his fire breath. In actual close combat, he has been seen chomping down on opponents within reach or powerfully swiping at them with his claws.
When entering his Human-Beast Form, Kaidou takes to wielding his kanabo, Hassaikai, like he does in his Human Form. With the boost he gains in strength, he can swing the club with extreme force, causing massive shockwaves and striking melee blows too dangerous for most enemies to take head on. Becoming far more agile than as a full dragon, Kaidou can move around by slithering through the air, using his dragon tail to propel himself forward or upwards, which aids his offensive moves. Moreover, his tail is prehensile and capable of capturing opponents off guard. Kaidou also demonstrates the ability to breath fire in his hybrid form, though with less force due to his decrease in size.
Once Kaidou acknowledges an opponent and gets drunk enough, he is able to engage in Shuron Hakke, an unique fighting style that takes advantage of Kaidou's drunken mood swings and allows him to quickly switch between his Zoan forms and employ more unpredictable techniques. During certain moods, Kaidou may even shift into completely unique forms outside his usual three. For example, while in a laughing or bloodthirsty mood, Kaidou manifests a bulkier version of his Human-Beast Form that can use stronger versions of his kanabo attacks, and while in a "thieving" mood, he turns into a smaller, slightly more humanoid variant of his Full Beast form that can swiftly fly around in sharp curves to dodge overwhelming enemy attacks.
Both in and outside of battle, Kaidou can create his "Flame Clouds" to use primarily as footholds or to levitate himself in order to take flight; he can thus easily travel between islands by flying quickly and crossing the open sea, such as between Onigashima and the Wano mainland. He can also levitate objects, even gigantic ones, by creating enough of his clouds to surround whatever he wishes to float away. This was chiefly seen when Kaidou sent the entire island of Onigashima aloft to proceed with his New Onigashima Project, levitating the island toward Wano's Flower Capital.
A sample of this Devil Fruit power has been extracted from Kaidou's Lineage Factor to be used as a template for Vegapunk's attempt at creating his own artificial Devil Fruit. Although he did manage to recreate the fruit, the project itself was deemed a failure.
- Bolo Breath (
熱息Boro Buresu?, literally meaning "Heat Breath"): Kaidou's most frequently seen attack, which has him gather fire inside his mouth before "breathing" it out into a huge, conical blast toward his target of choice. This blast travels rapidly (in the anime covering a tremendous distance within moments) and is extremely powerful. It can instantly decimate a large structure (like a castle's ruins) while leaving the surrounding terrain (like a mountaintop) blown to bits and scorched, can set a sizeable portion of a forest ablaze, and even be split into numerous smaller fireballs shot out like bullets. Despite this move's strength and scope, it can be countered by Foxfire Style. When Raizo cast this attack back at Kaidou via his scrolls, it proved able to somewhat damage the latter's own dragon body. Bolo is a term used in Central America and Mexico meaning "drunk". In the Viz manga, the technique is called Blast Breath.
- In the anime Kaidou is shown to be able to diffuse this attack into multiple smaller shots. This spreads out the damage and makes it harder to dodge, but also makes it significantly weaker than the original form. He used it against the Nine Red Scabbards in an effort to make them keep their distance.
- Kaifu (壊風 Kaifū?, literally meaning "Demolishing Wind"): An attack where Kaidou blows strongly, thereby creating powerful, crescent wind blades that can easily cut through solid stone as well as human bodies. The move was first seen being used in Kaidou's fight against the Nine Red Scabbards on the roof of Onigashima's Skull Dome, severing Kikunojo's left arm, but was not named until Kaidou used it against the Worst Generation members on the same roof. Denjiro described the wind blades as kamaitachi (かまいたち?), a Japanese term for cutting whirlwind derived from the yōkai Kamaitachi. The Viz Manga of the attack is Demolition Gust.
- Kaido is also capable of performing this move while in Human-Beast form. In this case, he quickly swings his Hassaikai to generate a vertical crescent-shaped wind blade that travels straight forward, akin to a Tobu Zangeki.
- Tatsumaki (龍巻 Tatsumaki?, literally meaning "Dragon Twister"): Kaidou spins his serpentine body into a coil to summon several tornadoes around him. Because of their wind speed, these tornadoes can pull people away from the ground and within Kaidou's range in midair, where he may chomp down on them. The technique was first seen in use against the Worst Generation members on the Skull Dome's roof. It was effective in capturing a defenseless Monkey D. Luffy, but Roronoa Zoro was able to neutralize it with his own Kokujo: O Tatsumaki technique. The name of the attack is the Japanese word for "tornado" (竜巻 tatsumaki?), but with the kyūjitai of the "dragon" (龍?) kanji instead of the shinjitai (竜?). In the Viz Manga, the technique is called Dragon Twister.
- Tatsumaki Kaifu (龍巻壊風 Tatsumaki Kaifū?, literally meaning "Dragon Twister Demolishing Wind"): An attack that combines Tatsumaki and Kaifu. Kaidou spins the lower portion of his elongated dragon body at great speeds, simulating a tornado himself. He then blows crescent wind blades towards his own spinning body, making the blades fly unpredictably in various directions. Kaidou also roars lightning while performing this technique, but that itself does not seem to be part of the attack. This move was first seen being used in Kaidou's fight against the Worst Generation. The Viz manga calls the attack Dragon Twister Demolition Breath.
- Kaen Daiko (
火龍大炬Kaen Daiko?, literally meaning "Fire Dragon Great Torch"): Kaidou breathes a large amount of flames from his mouth, forming a giant fire dragon over his original dragon body. The heat of his fire dragon near-instantly melts everything that it comes into contact with, preventing opponents from touching Kaidou, to which Luffy, a user of advanced Busoshoku Haki is able to counter this due to not having to make physical contact. The name of the technique is likely a reference to the rakugo story Kaen Daiko (火焔太鼓? "Flaming Drum"). In the Viz Manga, this is called Flame Dragon Torch.
On the day of the God Valley Incident 38 years ago at God Valley, Charlotte Linlin gave this fruit to Kaidou, who at the time was her crewmate on the Rocks Pirates. Big Mom considers this a debt for life that Kaidou cannot escape from.
Sometime within 34 years of him eating the fruit, Kaidou was in Marine captivity, and the scientist Vegapunk extracted his Lineage Factor for the purpose of creating an Artificial Devil Fruit. This replica fruit, while deemed a failure, was later eaten by Kozuki Momonosuke, shortly before the present day after having been stored on Punk Hazard. Momonosuke thereby gained a dragon transformation much like Kaidou's (even coming with the ability to produce Flame Clouds), albeit Momonosuke's power was initially out of his control.
- This fruit's name is currently the only Devil Fruit name with both its double syllables as vowel sounds with no consonant: "Uo" (ウオ?). Thus, it is (minus the "Model" designation) one of the shortest romanized Devil Fruit names.
- Ironically, despite a line of Zoan models being named after dragons (the Ryu Ryu no Mi) and this being the only known Devil Fruit ability to actually enable transformation into a dragon (the fruits of the Ryu Ryu no Mi series granting dinosaur/ancient reptile transformations), this fruit is not named after dragons but fish.
- While this fruit is classed as Mythical Zoan, with dragons explicitly stated as having mythical status in the One Piece world, dragons have also been real existences in the series, although modeled after Western dragons.
- Kaidou's dragon powers were first hinted at in the Punk Hazard Arc, as Kin'emon expressed deep resentment against one of Vegapunk's artificial dragons while fighting it, and when Brook commented that the samurai's hatred was reminiscent of someone trying to avenge their dead parents, Kin'emon replied that it was "nothing less", referring to Kaidou being responsible for his master Oden's death.
- According to Oda, Roronoa Zoro would have this Devil Fruit if he was allowed one, albeit "consumed" by one of his swords.
- Kaidou's teeth in his Human-Beast Form had a design discontinuity between chapters 1008 to 1010, and then 1011. Initially, while his upper canines became elongated fangs, Kaidou otherwise retained his angular human teeth. In the later design, the rest of his teeth became sharper and fang-like. However, the design was later reverted back to the original from Chapter 1016 onwards. That said, Kaidou does sport a full set of fangs when utilizing his alternate hybrid form.
- The Azure Dragon, in Chinese and other East Asian mythologies, is a Dragon God and one of the Four Symbols (the "Four Guardians") among the Chinese constellations, representing the cardinal direction of the East.
- With its "fish" designation, this fruit references the connections present between dragons and fish in East Asian (especially Chinese) mythology. Particularly, the fruit may draw inspiration from the Chinese Dragon Gate myth, wherein the Dragon Gate is located atop a waterfall cascading from a legendary mountain, on the Yellow River. Many carp swim upstream against the river's strong current, but few are capable or brave enough for the final leap over the fall. If a carp successfully makes the jump, it is transformed into a majestic dragon; thus, a Chinese dragon's large, conspicuous scales indicate its origin from carp.
- Kaidou's dragon form has four claws/toes: four-clawed dragons are customarily depicted in Mongolia and Korea (as opposed to the three claws common for Japanese dragons). In China during the imperial dynastic era, four-toed dragons symbolized imperial aristocracy (e.g., princes), denoting imperial ranking just below the emperor himself, who is symbolized by five-toed dragons.
- Eastern dragons that breathe fire are minor in lore. Those who do were said to be rather violent or sent from the heavens to earth as punishment. Kaidou's ability to breathe a fire blast (contrary to the Eastern dragon's prevalent water association) is likely inspired by European conceptions of fire-breathing dragons or "firedrakes".
- Befitting Kaidou's title as the world's "Strongest Creature", Asian dragons (particularly Chinese dragons) are noted to be extremely powerful mythical beasts in Asian mythology, some even deified as gods in heaven and worshipped as such in Chinese myth.
- When Kaidou first appeared in his dragon form, he did so by emerging through dark, swirling clouds in the sky. This may be inspired by dragons in Utagawa Kuniyoshi's ukiyo-e paintings, as well as the dragon Shenron from the Dragon Ball franchise. In both cases, dragons' arrival is accompanied by dark clouds covering the sky.