The Ryu Ryu no Mi, Model: Pachycephalosaurus is an Ancient Zoan-type Devil Fruit that allows the user to transform into a hybrid and full version of a pachycephalosaurus at will. It was eaten by Ulti.
Ryū (竜,Ryū?) is Japanese for "dragon" and can be found in the Japanese term for "dinosaur" (恐竜,kyōryū?).
Strengths and Weaknesses
This fruit's power is to turn into a full and hybrid version of a pachycephalosaurus: a bipedal, herbivorous dinosaur distinguished by its super-thick, durable skull roof. The Human-Beast Form already grants a significant increase in body size, with Ulti going from an ordinary height to over three times as tall, and her full Beast Form is even bigger, at least as large as her brother's full spinosaurus form.
Much like other fruits of the Ryu Ryu no Mi series, this one grants its user a tremendous increase in physical strength. In spite of having proportionally smaller arms, Ulti is able to hold targets down in her full pachycephalosaurus form, shown when Monkey D. Luffy, despite being tremendously strong himself, found himself immobilized by Ulti's claws grabbing his shoulders and considered activating Gear Fourth to escape her clutches. Beside strength, the user, in their less heavy hybrid form, becomes much faster, especially due to their strengthened dinosaur legs. Ulti is able to dart through the air at extreme speed by jumping, while proportionally increasing the impact force of her attacks in the process, and can casually dodge extremely fast-moving attacks, disappearing from sight.
With the transformation, the user's skull grows thicker and harder, which suits Ulti particularly given her fighting style that revolves around headbutts. While transformed, her large skull dome (more so her forehead in hybrid form) allows Ulti to potentially crush opponents' skulls completely with headbutts, like she already can in human form, strike large animals unconscious, as well as break through thick stone walls by charging into them headfirst.
Moreover, the user's transformation dramatically boosts their endurance and speed of recovery, a characteristic trait of dinosaur Zoans. After Ulti had been knocked out (in Beast Form) by Yamato's Raimei Hakke, a surprise attack hitting her head, Ulti was quick to regain her consciousness, seeming unaffected beside bleeding from the mouth. Another time, Ulti took a direct hit from Nami's Thunder Lance Tempo, the lightning bolt piercing her abdomen, but retained consciousness, only falling to the ground in pain; Nami, in said instance, mentioned how a much stronger lightning was necessary to put down Ulti.
No weaknesses of the fruit's power are of note, beside the standard Devil Fruit weaknesses.
Ulti uses this fruit for combat. Already a strong melee fighter while human, Ulti can dramatically strengthen her physical attacks by transforming, namely her headbutts. Ulti's full pachycephalosaurus form is considered excessive to use against most opponents, likely to cause great collateral damage, with both her hybrid and full dinosaur forms only unleashed by her against enemies whom she takes seriously.
While transformed, Ulti has shown a penchant for holding down enemies with both hands to ensure her ability to land a headbutt.
Ul-Zugan (ウル頭銃,Uru Zugan?, Literally meaning "Ul Head Gun"): Ulti's basic headbutting move where she covers her forehead with Busoshoku Haki, then slams her head into that of her opponent to, ideally, crush their skull. When using the attack in her Human-Beast Form, its power is greatly increased, and she can take advantage of her heightened leg strength in order to launch herself headfirst into a given target, at great speed. In the Viz translation and Funimation subtitles, the attack is called Ulti-Mortar.
Ul-Meteor (ウル頭銃群,Uru Mītia?, literally meaning "Ul Head Gun Group"): While keeping hold of her opponent, Ulti rears her head back to prepare unleashing a headbutt in what is seemingly an upgraded version of her Ul-Zugan. Ulti was first shown trying to use this technique on Luffy but was unable to execute it, due to being surprise-attacked by Yamato. Since Ulti was attacked in the middle of saying the attack name, "Ul-Meteor" may not be the full name. In the Viz translation and FUNimation subtitles, the attack is called Ulti-Meteor.
The thick skull dome of the Pachycephalosaurus (and of other pachycephalosaurid genera) has given rise to the hypothesis of pachycephalosaurs having used their skulls in intra-species combat, via headlong ramming, something obviously played on in-story by Ulti's headbutting.
This hypothesis, however, has been disputed for some time, with the main argument raised against the possibility of headbutting pachycephalosaurs being that their skull roof may not have adequately sustained impact associated with ramming, as well as the lack of definitive evidence of scars, or other damage, on fossilized Pachycephalosaurus skulls that was intially present. However, analyses from more recent (from 2012 onward) cranial pathology studies about pachycephalosaurs have uncovered such damage: a high rate of lesions in pachycephalosaurid skull domes.
Ulti grows noticeably larger in both her Human-Beast and, even more so, her full Beast Forms, despite the pachycephalosaurus being known to have stood shorter than the average human.
In the manga, Ulti's Beast Form appears to change her hair color, turning it from a darker to a much lighter shade.
Ulti's dinosaur skin is differently colored in her Vivre Card entry compared to the anime; in the former, it is brownish-orange while in the anime, it is yellow-green.
In the anime, the irises of Ulti's eyes turn red when she uses her transformation.
↑One Piece Manga — Vol. 99Chapter 995 (p. 16), Ulti in her hybrid is over three times bigger than Nami, who is about the same height as her in human form, to the point that Ulti can hold Nami in one hand.
↑ 3.03.13.2One Piece Manga — Vol. 99Chapter 998 (p. 16-17), Ulti in her full Beast Form is shown next to Page One's full spinosaurus form, both breaking through a wall.