Reginald Kastle

For the other character who used the name "Nasch" as an alias, see Dumon.

"Reginald" redirects here. For the Yu-Gi-Oh! GX character, see Reginald Van Howell III.

"Shark" redirects here. For the archetype, see Shark (archetype).

{{Infobox character | headers = yes | image =

• 

  Reginald Kastle/Nasch's true form

• Kamishiro Ryoga.jpg

  Reginald Kastle/Nasch's human form

• * Nasch (ナッシュ ''Nasshu'')
• ==Design==
• ===Appearance===
• ===Personality===
• ===Abilities===
• ===Etymology===
• ==Biography==
• ===History===
• ====Past life====
• ====Current life====
• ===Yu-Gi-Oh! ZEXAL===
• ====Pre-World Duel Carnival====
• ====World Duel Carnival Preliminaries====
• ====World Duel Carnival Finals====
• ===Yu-Gi-Oh! ZEXAL II===
• ====Barian Invasion====
• ====Legendary Number War====
• ====Barian Emperor Onslaught====
• ==Other appearances==
• 

  Ryoga Kamishiro (manga)

• 

  Ryoga Kamishiro (D Team)

• 

  Reginald Kastle (Clash! Duel Carnival!)

• 

  Shark (Duel Terminal)

Relationships

Rio Kastle

Shark and Rio are twins and share a strong bond ever since they were children, symbolized by matching rings that Rio obtained. Following Rio's Duel with Quattro, in which she was critically injured and wound up in a hospital bed wrapped in bandages, Shark Dueled in the National Duel Circuit for her sake, but pressure was escalated to such an extent that he peeped at his opponent's Deck before the final match, an action that caused him to be disqualified and banned. During the time Rio was in the hospital to recover from her injuries, Shark often visited her.

Despite their bond, Shark has a typical tenuous "brother-sister" relationship with Rio, irritating one another and having normal siblings squabbles. They seem to settle any fighting by Dueling each other, having a total of one-hundred Duels.

Their bond is incredibly strong, with brother and sister remaining close over many of their lives with Rio supporting and standing by her brother's side ruling together with him as Merag in their original human lives, as well as again after returning to being Barians.

Yuma Tsukumo

Shark and Yuma's first encounter.

Shark first met Yuma Tsukumo when he came to defend Bronk Stone after he beat him in a Duel and took his Deck. In a twist of events, Shark crushed the Emperor's Key and accepted Yuma's challenge, becoming rivals with the young boy. With their Duel underway, Shark was overtaken by "Number 17: Leviathan Dragon" and quickly Summons it to put Yuma in his place. However, with the appearance of Astral and Yuma's new Xyz Monster, "Number 39: Utopia", Shark loses the Duel and his "Number".

Soon after, Shark falls into the "wrong crowd" and stops Dueling all together, but with persistence from Yuma, Shark agrees to Duel him again. Despite his "Numbers", Yuma loses to Shark, who then tells him to never interfere with his life. However, Yuma disobeys this after learning of why Shark was the way he was. The two then have a Tag Duel against Scorch and Chills, also carried "Numbers" that supported each other. Despite that, Shark was able to aid Yuma, who protected him from any damage, and give him the final trump card that would defeat the two brothers. As a sign of respect for Yuma, he allowed him to keep the card he won with.

Mr. Kay made a remark that Shark had changed due to Yuma's influence and now he sees Yuma as a friend and ally. Although friends, Shark doesn't hang around Yuma as much as his other friends, due to his aloof nature, but is shown to have a soft spot for him. In addition, Shark often reflects on his time with Yuma, even watches Yuma from afar when he sees him. Despite his distant nature, Shark is willing to open up to him (to an extent), but tends to push him away sometimes. In turn, Yuma admires Shark and worries about him if he does anything he thinks is wrong or dangerous. When knowing things concerning Shark, Yuma would focus his attention on helping him and putting himself in harm's way, even sometimes ignoring or lashing out on his friends or Astral if they tried to stop him.

Throughout the World Duel Carnival, their friendship becomes strained as Shark became focused on revenge on Quattro and continually told Yuma "Don't get involved with me" when they met. When Yuma learns how violent Shark had become, Yuma challenged him to a Duel, in which Yuma made no move to attack, and let Shark take his anger out on him. He was angry at Yuma's persistence and the Number's influence causes him grow more aggressive. Eventually, Yuma tells Shark he doesn't want to see the way he is now, shocking him, and is followed by his stomach growling. As Shark watches Yuma and Tori shout at each other, he smiled and the darkness in his heart disappeared. Shark then cancelled the Duel, claiming that seeing Yuma being an "idiot" made him lose his drive. Before walking away, Shark tells Yuma that he would meet him in the finals and they exchanged smiles.

During the WDC party, Yuma tried looking for Shark, showing his concern for Shark, and because he has something to ask him, but couldn't find him. During the finals of WDC, Yuma stumbles across Shark's Duel with Quattro and stayed to cheer him on. When Shark Summoned "Number 32: Shark Drake", Yuma worried about him due to the influence of the "Number", and cried out to Shark as he was brutally attacked eight times by Quattro. As the Duel continues, Yuma tried to pull Shark away from the influence of the "Number", but Shark eventually gives into it. After Shark wins the Duel, Shark set his revenge on Vetrix and told Yuma he won't forgive him if got in his way, straining their friendship once again.

In the semi finals, Yuma and Shark were matched-up to Duel each other, with Yuma eager to settle their rivalry. Unknown to Yuma, Vetrix was influencing Shark through the power of his crest, but Yuma does notice how emotionless and different Shark is. During the Duel, Vetrix made Shark think Yuma was the one to hurt his sister, which made Shark hate Yuma and attack him ruthlessly. Yuma tried to make Shark remember the times they Dueled together, how Shark tried protecting his Emperor's Key from Kite, and how much their bond means to him. Yuma also told Shark that his goal is to be Duel Champion and defeating Vetrix and Dr. Faker wasn't worth losing him. To return Shark to normal, Yuma took control of "Number C32: Shark Drake Veiss" and suffered while the "Number" tried to control him. Shark was able to regain his senses and begins to worry for Yuma. When deciding to save Shark or Astral, Yuma couldn't choose and said that Shark is a very important friend to him. To save Yuma, Shark got rid of his remaining Life Points to banish "Shark Drake" and give Yuma the victory. Afterwards, Shark told Yuma how during the Duel that he could hear Yuma's voice and thanked Yuma for saving him. Smiling, Shark then encourages Yuma to win and beat Vetrix, with Yuma promises to carry on his will.

Later, when Shark awakes in the hospital and sees that Yuma's Dueling with Vetrix in the Sphere Field, he begins to worry and rushes over to the Duel Coaster Stadium, calling out Yuma's name as he goes.He then enters Heartland Tower to save Yuma and puts himself in danger in the process, showing how much he cares for him. Shark was even willing to team up with Kite and Orbital 7 to rescue Yuma, despite his hostility towards them. When Yuma challenges Dr. Faker to a Duel, Yuma gave back Shark "Number 32: Shark Drake", asking him to help him, and the latter joins Yuma with a smile. During the Duel, Yuma and Shark supported each other well with their cards, as well as Shark teasing Yuma when he's getting doubts. When the Heartland Tower started to crumble, a piece of concrete was about to hit Yuma before Shark pushes him out of the way to protect him, taking the hit instead.

When the Barian World began to target Yuma for the "Numbers", Shark worried for Yuma's well-being and chases after him when he goes to Duel Fender, even leaving his sister to go after him. When talking to Rio, Yuma learned that Shark often talked about him to her, to his surprise. She told Yuma that she believed it's because of Yuma that her brother hadn't changed and thanked him for being a good influence on Shark. Also, Shark began to spend more time with Yuma as they started to walk home together after school. When Yuma fell towards a cliff ledge, Shark once again put his life in danger to try to save Yuma from falling,. Recuperating in the hospital, Shark was extremely upset how downhearted Yuma was acting and, in his typical gruff fashion, snapped at him. In order to get through to him, Shark swiped the Emperor's Key and lured Yuma into a Duel. With help from Astral, Yuma got his fighting spirit back, much to Shark's happiness. When Astral told Yuma what Shark's true purpose was, Shark denied it, but Yuma was greatly touched. Trying to show his gratitude, Yuma tried to give Shark a hug, only to be pushed away by him.

After Shark came to accepting his fate as a Barian, he was emotionally shattered at the thought of becoming Yuma's enemy and distraught of breaking his bond and friendship with him.

Despite initially being shattered at the thought of Yuma becoming his enemy, Nasch had no problems with trying to attack Yuma when he returned to Earth, even going as far to Duel him for his "Numbers".

Astral

At first, Shark had no knowledge of Astral, but Astral has respect for Shark's Dueling skills and the impact he has on Yuma.. If Shark becomes possessed by a "Number" card, Astral and Yuma usually come into conflict with Shark and try to save him from the card's dark influence.

Sometime between Shark and Yuma becoming friends and the World Duel Carnival, Shark's learned of Astral's existence and knows how important he is to Yuma. Knowing Shark is trustworthy and strong-willed, Astral has no problems letting him keep "Number 32: Shark Drake" card in his possession. After the Duel with Vector, Shark can now see and hear Astral, but they still have little contact with each other.

Kite Tenjo

Having heard about the "Number Hunter", Shark already knew Kite's reputation, but officially met him when he stopped Orbital 7 from killing him and demanded that Shark hands over the Emperor's Key. Shark figured out that Kite was the "Number Hunter" and his intentions towards Yuma, then lied about having a "Number" card. This resulted to a Duel between them, where Kite easily defeated Shark, taking the key and the latter's soul. Shark bared a grudge against Kite since then, and meeting again in Heartland Tower, he was very hostile to Kite, though he did help free him from the rubble that had trapped him. However, Kite didn't care about it as his little brother, Hart, was in trouble and told Shark they could have a rematch later. After arguing, the two agreed to work together to save Yuma and Hart.

During the Duel with Dr. Faker, they developed a friendship and worked well with each other. Although Shark holds little contact with Kite, they come together if the Barian World poses a big enough threat, but they have a tendency to argue with one other. Initially, Kite refereed to Shark by his first name, but as they were around each other more often, he began using Shark's nickname just as others do.

Though despite their differences, both he and Kite are a lot alike, both do whatever they can to protect their siblings (Hart and Rio) and become quite vengeful and angry with both are in danger, as well as both seem to posses cool and distant personalities.

Quattro

Shark's earliest acquaintance with Quattro was at the National Duel Circuit , where he was Shark's opponent in the final match, which he won by disqualification. He becomes Shark's target of revenge when he revealed that he set Shark up for disqualification by placing his Deck so that Shark could see it, and was the one responsible for Rio's injuries. Shark entered the World Duel Carnival in order to get revenge on Quattro, spending most of the time pursuing him. When they do meet, Quattro takes pleasure out of mocking Shark and provoking him, as it was part of the his family's plans to use Shark and make his hatred grow.

However, Quattro developed jealously towards Shark once he found out that Vetrix wanted Shark to defeat Dr. Faker instead of him. At the WDC party, Quattro confronted Shark out of anger, only to grow more irritated when Shark mocked him before leaving. In the finals, they continued to provoke one another as Quattro led Shark to the "Magma Field" field for their rematch Duel. Out of frustration, Quattro brutally Dueled against Shark to show his father that he was better than him. After Quattro lost to Shark, he apologized for his misdeeds and entrusted Shark with the task of defeating Vetrix, which only annoyed Shark. His revenge and anger then shifts to Vetrix, as he was the one who orchestrated the whole thing.

Shark later reunited with Quattro when he came to help him with Duel against Kurage and teamed up him. The two rivals developed a level of camaraderie, although they often trade insults to each other, which made Trey commented that it was hard to figure out if they were on good or bad terms.

Later Quattro dueled against Shark, now Nasch, in order to buy some time for Yuma to escape, Quinton commented that Shark was Quattro's "only true friend" and Quattro stated that he would do what Yuma did, bring back his bonds.

Dumon

During his tenure as King of the United Lands of the Poseidon Ocean, he had befriended a knight from another kingdom. This knight, Dumon, had become close with Nasch, swearing to defend and fight alongside him and his enemies.

Their friendship even continued on to their next lives, when the two men had been reincarnated as Barians where Dumon would continue to serve Nasch once again. Even after Nasch had supposedly disappeared from the Barian world, Dumon (now leader of the other Barians) held on to the hope their leader would return one day. Once Vector had mentioned the possibility of their lost leader being on Earth, Dumon became absolutely determined to find and bring his leader back.

Once it became apparent that Nasch was indeed the human Shark, Dumon was able to convince him it was his destiny to join the Barians, and finally Nasch had joined up with him once again.

Decks

Main article: Reginald Kastle's Decks

Shark plays a Xyz WATER Deck consisting of monstrous looking sea creatures such as various races of sharks. He utilizes a Burn strategy in order to quickly gain the advantage through cards such as "Submersible Carrier Aero Shark" and "Explosive Urchin", with a focus on using Level 3 monsters, such as "Big Jaws" to Xyz Summon Rank 3 Xyz Monsters.

Shark uses cards that can counter "Numbers", whether that be negating their effects with "Black Ray Lancer" or taking control of them with "Splash Capture". As his Xyz Monsters are Rank 3, their ATK tends to be on the lower side. He includes cards to decrease the ATK of his opponent's monsters such as "Needle Sunfish" and "Friller Rabca" to make up for this. A cautious Duelist, he includes many cards to counter Spells and Traps, such as "Sea King's Verdict", "Mystical Space Typhoon", "Plate Salvage" and "Skull Kraken".

After acquiring "Number C32: Shark Drake Veiss", Shark's Deck shifted to include more Level 4 monsters in order to Summon "Number 32: Shark Drake" and became more focused on the "Shark" archetype. Similarly, after acquiring "Number 94: Crystal Zero the Polar Ice Princess" and "Number 73: Abyss Splash the Roaring Waterfall Deity", his Deck shifted to include more Level 5 monsters.

When Shark became Nasch he seemed to use the same deck as when he was human, however now being a Barian he also has access to his "Number 10X" Number as well as the Chaos Number tied to it and the Rank-Up spell card exclusive to the Barian Emperors.