{{Redirect|Reginald|the ''[[Yu-Gi-Oh! GX]]'' character|[[Reginald Van Howell III]]}}{{Redirect|Shark|the [[archetype]]series|[[Shark (archetypeseries)]]}}

* "Shark" Kamishiro<ref>{{cite web|url=http://affiliate.zap2it. com/tv/yu-gi-oh-zexal/cast/EP01482633|accessdate=September 1, 2012|title=''Yu-Gi-Oh! ZEXAL'' Cast|publisher=ktla.com|archive-url=http://web.archive.org/web/20151106193132/https://affiliate.zap2it.com/tv/yu-gi-oh-zexal/cast/EP01482633|archive-date=November 6, 2015}}</ref>

| en_voice = {{voice actors|en|Gary Mack}}<ref>{{cite web |title=Reginald "Shark" Kastle Character Profile |url=https://yugioh.com/characters/shark |website=Official Yu-Gi-Oh! Site |access-date=15 June 2022 |language=en}}</ref>

'''Reginald Kastle''', known as '''Ryoga Kamishiro''' ({{Ruby|神|かみ}}{{Ruby|代|しろ}} {{Ruby|凌|りょう}}{{Ruby|牙|が}}, ''Kamishiro Ryōga'') in the manga and Japanese version and nicknamed "'''"Shark"''' " (シャーク, ''Shāku'') in all versions, is one of the main characters in ''[[Yu-Gi-Oh! ZEXAL]]''. He is one of [[Yuma Tsukumo]]'s close friends and rivals. He was originally an arrogant and callous person, but has grown quite humble. He is later revealed to be the reincarnation of '''Nash''' ('''Nasch''' (ナッシュ, ''Nasshu'') in the Japanese version), the leader of the [[Seven Barian Emperors]]. Determined to not let tragedies befall his people again, he betrayed Yuma and his friends to safeguard the [[Barian World]]. He is the only Barian Emperor not to be absorbed by Don Thousand, as well as the only Barian whose original memories were not altered. He later vanished after losing to Yuma in a Duel that had the Human, Astral and Barian Worlds at stake. He, along with the [[Seven Barian Emperors]], were revived by the [[Numeron Code]].

<div style="float:right">[[File:NashLineart.jpg|thumb|140px|right|Nash's lineart]]</div>

<div style="float:right">{{triple image|right

|Full -body view of Shark in his past, present , and Barian forms.}}</div>

An unknown number of years later, [[Don Thousand]] reincarnated both he and his sister as two of the [[Seven Barian Emperors]], as their souls were each connected to a [[Mythyrian Number|Mythyrian "Number"]] card, which had sealed Thousand's power.<ref name="ep129">{{episode|Yu-Gi-Oh! ZEXAL|129|ref}}</ref> Nash then became the leader of the Seven Barian Emperors, much to Vector's disdain (also having been reborn as a Barian Emperor). After Nash had annoyed him enough to score 100,000,000 (1,000,000 in the dub) points, Vector enacted his revenge by taking Marin hostage. When Nash intervened, Vector used "[[Giant Sky Sword]]" to open a bottomless rift and then pushed Marin from the cliff, forcing Nash to dive after her, only for the two to be sucked into the rift. The two were rescued by Abyss, who informed them that he would send them to the Human World without their memories, where their souls were then revived in the bodies of [[Reginald Kastle (original)|Reginald]] and [[Rio Kastle (original)|Rio Kastle]], both who were pronounced dead in a car accident.<ref name="ep131">{{episode|Yu-Gi-Oh! ZEXAL|131|ref}}</ref> While Vector believed them dead,<ref name="ep109" /> Dumon believed they had simply disappeared and assumed leadership of the group from them in the interim, waiting for their return.<ref name="DurbeInfo">{{citewebcite web|url=http://www.tv-tokyo.co.jp/anime/yugioh-zexal/images/chara_barian.png|title=TV Tokyo's Barian profile|publisher=tvtokyo.com}}</ref>

When Nash arrived, he fired a lightning bolt at Vector in a rage. They began their Duel, with Vector having brought the [[Number ruins|ruins]] from his past life into the Barian World to serve as their arena. Vector used "[[Contract with Don Thousand]]" to give Nash a handicap, with Nash proceeding to fall into his trap and attack with "Silent Honor DARK" after Summoning it with "The Seventh One". Using a combination of "[[Chaos Rising]]" and "[[Chaos Caller]]", Vector brought out "[[Number C65: King Overfiend (anime)|Number C65: King Overfiend]]", "[[Number C104: Umbral Horror Masquerade (anime)|Number C104: Umbral Horror Masquerade]]", "[[Number C102: Archfiend Seraph (anime)|Number C102: Archfiend Seraph]]" and "[[Number C103: Ragnafinity (anime)|Number C103: Ragnafinity]]". Yuma arrived to support Nash at this point, but Nash persisted that they were enemies now. Vector used the power he had gained from the other Emperors to gain a new form. Nash survived Vector's assault with 100 Life Points and launched a counterattack using "[[Split Defender]]" and "[[Xyz Charge Up]]", ultimately resulting in him taking control of "King Overfiend" and using it to destroy "Umbral Horror Masquerade". This triggered Vector's true memories.<ref name="ep136"/> Once he remembered, Vector claimed to have realized the error of his ways, and activated "[[Xyz Discharge]]", allowing Nash to seize control of his comrades' "[[Number C10X|Chaos Over-Hundred Number]]s" at the cost of sending a card in his hand to the Graveyard. Attacking at Vector's wishes, he fell into his trap, "[[Trick Buster (anime)|Trick Buster]]", which destroyed all of Nash's monsters and dealt him 300 damage for each monster destroyed. However, Nash avoided the damage by activating the effect of his "[[Dream Shark (anime)|Dream Shark]]". Vector, who was surprised to see him survive, accused Nash of not trusting him to start with, with Nash responding that he discarded the ability to trust when he shed his humanity. As the battle waged on, Vector performed a direct [[Chaos Xyz Evolution]], Summoning "[[Number C5: Chaos Chimera Dragon (anime)|Number C5: Chaos Chimera Dragon]]" with the effect of "[[Rank-Up-Magic Admiration of the Thousands (anime)|Rank-Up-Magic Admiration of the Thousands]]", using "Chaos Numbers" in the Graveyard as Overlay Units. This card nearly defeated Nash, but he survived with "[[Depth Gardna]]" and then used "[[Infinity Tooth]]" to counter Vector's manipulation of his draws. He performed a second Chaos Draw and used the resulting "[[Depth Biter]]" to Summon "[[Number 73: Abyss Splash (anime)|Number 73: Abyss Splash]]". Though Vector countered with "[[Overlay Burglary]]", Nash revealed a second "[[Rank-Up-Magic]]" in the form of "[[Rank-Up-Magic Quick Chaos (anime)|Rank-Up-Magic Quick Chaos]]", creating "[[Number C73: Abyss Supra Splash (anime)|Number C73: Abyss Supra Splash]]" and defeating Vector.<ref name="ep137"/>

As Vector went berserk with his power, Nash was surprised when [[Don Thousand]] appeared before them and tried to absorb Vector. He showed a little concern when Yuma ran to try and save Vector, urging Yuma to stop and that Vector had no soul; even if Yuma did save Vector, Vector would backstab him again. After Vector let himself be absorbed to protect Yuma and Don Thousand assumed his true form, Mizar arrived and Nash watched the Duel between him and Don Thousand. When Mizar lost, Nash mourned his death, which left him as the last of the Seven Barian Emperors. With his new form, Don Thousand stated that he will absorb Nash as well and challenged him and Yuma to a Duel. To avenge his comrades, Nash agreed to team up with Yuma against Don Thousand. Thousand quickly negated Yuma's Summon of "[[Number 39: Utopia (anime)|Utopia]]," revealing that the merging of the Barian and human Worlds was to enable him to control the [[Numeron Code]], allowing him to attack the Astral World directly.<ref name="ep138"/> Using his "[[Numeron]]" monsters, Thousand nearly defeated them, with Yuma and Nash surviving with "[[Half Unbreak (anime)|Half Unbreak]]" and "[[Cutter Shark (ZEXAL anime)|Cutter Shark]]". Astral left to find the location of the "[[Numeron Network (anime)|Numeron Network]]" card to help them. Nash baited Thousand into using "Numeron Network" to rewrite his "[[Aqua Jet (anime)|Aqua Jet]]", allowing him to use "Rank-Up-Magic - The Seventh One" to bring out both his "Over-Hundred Number" and its "Chaos" form. Thousand survived with "[[Numeron Wall (anime)|Numeron Wall]]", but by then Astral had found "Numeron Network" and put it onto the field, resulting in Nash destroying it with "[[Depth Eruption]]". Nash was tearful when it appeared that Astral would sacrifice himself to keep the resulting energy from destroying Earth, but [[Eliphas]] appeared and sacrificed himself in Astral's place.<ref name="ep139">{{episode|Yu-Gi-Oh! ZEXAL|139|ref}}</ref>

Yuma and Nash worked well together, with their combinations nearly defeating Thousand several times. However, Thousand countered with "[[Number C1000: Numeronius (anime)|Number C1000: Numeronius]]", whose effects controlled nearly the entire field. Nearly defeated, Kite's spirit appeared to Yuma and Yuma was able to counter with "[[Number 100: Numeron Dragon (anime)|Number 100: Numeron Dragon]]". This play forced Thousand into his final trump card, "[[Number iC1000: Numeronius Numeronia (anime)|Number iC1000: Numeronius Numeronia]]". The card could not attack, but essentially put a timer on the Duel - if they did not attack it next turn, Thousand would [[Victory Condition|win automatically]]. Yuma activated "[[Session Draw]]", letting both of them draw during Nash's next [[Draw Phase]]. If the monsters drawn were of the same Level, they could Xyz Summon using them. Yuma used [[Shining Draw]], while Nash used Chaos Draw, allowing them to use "[[ZW - Tornado Bringer (anime)|ZW - Tornado Bringer]]" and "[[Panther Shark (anime)|Panther Shark]]" to bring out "Abyss Splash". Yuma's "[[Utopia Rising]]" and "[[Bonds of Hope]]" Trap Cards further augmented "Utopia" with the effects of "Abyss Splash" and "Numeron Dragon".<ref name="ep140">{{episode|Yu-Gi-Oh! ZEXAL|140|ref}}</ref>

Nash set up the return of "Barian Hope" with "[[Reincarnation of the Seven Emperors (anime)|Reincarnation of the Seven Emperors]]" before Summoning "[[Black Ray Lancer (anime)|Black Ray Lancer]]" in an attempt to defeat Yuma. Yuma countered with the effect of "Utopia Beyond", Summoning "Utopia" again. Nash weakened "Utopia" with "[[Friller Rabca (anime)|Friller Rabca]]" and brought out "[[Submersible Carrier Aero Shark (anime)|Submersible Carrier Aero Shark]]" as well, but Yuma survived with "[[Damage Take-Over]]". Using ZEXAL, Yuma and Astral created "[[ZW - Sylphid Wing (anime)|ZW - Sylphid Wing]]", but Nash revived "Barian Hope" using "[[Rebirth of the Seven Emperors (anime)|Rebirth of the Seven Emperors]]" at the expense of his Rank 3 monsters. Yuma pushed the attack, but Nash used "[[Draw of Fate (anime)|Draw of Fate]]" to negate the attack and force both players to draw a card. If the player did not use the drawn card by the end of this turn, they would [[Victory Condition|automatically lose]]. Nash used Chaos Draw to draw "[[Glory of the Seven Emperors]]", while Yuma used Shining Draw to draw "Double or Nothing!" Yuma canceled his attack after activating "Double or Nothing!", knowing that defeating Nash would be to sacrifice who Yuma had been, just as [[the Door]] had predicted. Nash had known he would "Double or Nothing!", but this action was not predicted. "Glory of the Seven Emperors" would have allowed him defeat Yuma had Yuma done anything else, but canceling his attack resulted in Nash's Life Points becoming 0. Nash told Yuma never to lose what was most important to him - his ability to believe in others and his pure heart. He mused that he'd not see the future they would create though. The "Numbers" flooded from Nash's body and were absorbed by Astral. Nash told Tori to never let Yuma out of her sight and called Yuma and Astral the best friends he'd ever had. He informed them that he considered this final Duel to be his greatest - and also the most enjoyable. Nash succumbed to his wounds after this, fading away.<ref name="ep143" />

After defeating [[Don Thousand]] alongside Yuma, Nash absorbed all of Thousand's "Numbers". Among them were "[[Number 1: Numeron Gate Ekam (anime)|Number 1: Numeron Gate Ekam]]", "[[Number 2: Numeron Gate Dve (anime)|Number 2: Numeron Gate Dve]]", "[[Number 3: Numeron Gate Trini (anime)|Number 3: Numeron Gate Trini]]", "[[Number 4: Numeron Gate Catvari (anime)|Number 4: Numeron Gate Catvari]]", "[[Number 5: Doom Chimera Dragon (anime)|Number 5: Doom Chimera Dragon]]", "[[Number 6: Chronomaly Atlandis (anime)|Number 6: Chronomaly Atlandis]]", "[[Number 9: Dyson Sphere (anime)|Number 9: Dyson Sphere]]", "[[Number 33: Chronomaly Machu Mech (anime)|Number 33: Chronomaly Machu Mech]]", "[[Number 43: Manipulator of Souls (anime)|Number 43: Manipulator of Souls]]", "[[Number 46: Dragluon (anime)|Number 46: Dragluon]]", "[[Number 58: Burner Visor (anime)|Number 58: Burner Visor]]", "[[Number 62: Galaxy-Eyes Prime Photon Dragon (anime)|Number 62: Galaxy-Eyes Prime Photon Dragon]]", "[[Number 64: Ronin Raccoon Sandayu (anime)|Number 64: Ronin Raccoon Sandayu]]", "[[Number 65: Djinn Buster (anime)|Number 65: Djinn Buster]]", "[[Number 80: Rhapsody in Berserk (anime)|Number 80: Rhapsody in Berserk]]", "[[Number 96: Dark Mist (anime)|Number 96: Dark Mist]]", "[[Number 102: Star Seraph Sentry (anime)|Number 102: Star Seraph Sentry]]", "[[Number 103: Ragnazero (anime)|Number 103: Ragnazero]]", "[[Number 104: Masquerade (anime)|Number 104: Masquerade]]", "[[Number 105: Battlin' Boxer Star Cestus (anime)|Number 105: Battlin' Boxer Star Cestus]]", "[[Number 106: Giant Hand (anime)|Number 106: Giant Hand]]" and "[[Number 107: Galaxy-Eyes Tachyon Dragon (anime)|Number 107: Galaxy-Eyes Tachyon Dragon]]". Many of these also had "[[Number C]]" forms, including the "[[Number 10X|Over-Hundred Numbers]]". In addition, there was "[[Number C1000: Numeronius (anime)|Number C1000: Numeronius]]" and "[[Number iC1000: Numeronius Numeronia (anime)|Number iC1000: Numeronius Numeronia]]", which lacked a base "Number" form.<ref name="ep141">{{episode|Yu-Gi-Oh! ZEXAL|141|ref}}</ref>