Shark is a nick name for Reginald kastle or his name in the manga is ryoga kamishiro and he is from yu-gi-oh zexal so this will give us information about him.
Yu-gi-oh zexal
Shark was a barian in his past but he was a ruler who fight against vector in their past but they were having human forms he with his tribe and sister fought until one day he lost but rio tried to help them if vector kills a human to bring number 73 abyss splash then if she gives up her life it would disappear however ryoga was sad and fought back for his sister and won but while searching for vector after their lose he found a girl called chirashca she was crying it was like she was his sister the same face hair and every thing he was with her shark is an orphan his parents died when he was young .he grew up in the orphanage with his sister rio. he was with his friend kyougi like shadow and light but not in bad things.
once he and his sister was in a carnival .rio found a piar of grey rings they were similar then she asked her brother to have one but he refused.
but later his sister was hurted by an fire accident but Quattro saved her from the fire but hark thinks that Quattro is the one who harmed her because the fire was caused by her duel with shark go to the hospital as a visit but she told him to win for her in the national duel circuit against Quattro.
but there while shark was surrounded by the pressure of his old did not know that Quattro set him up by putting his deck on the edge of the flower vase so it falls when shark saw what happened he saw his deck by a mistake but accually he saw one card that was mirror force when he was duelling against his opponent Quattro it was going to win but he knows that if he attacks Quattro will activate his trap card but suddenly he relized the card mirror force now he knew what I his trap card but he disqualified during the duel and in that moments he stops the duel and everyone knew that he cheated and Quattro became the winner
. now shark has 14 years old he goes to school but he was cold and careless and he was the bully of the shark is not his real name it is a nick name for him but most of the people are calling him shark his real name is Reginald and he got his nickname from people because his deck was xyz sharks and his clothes and hairstyle and accissories was referring to shark but later Reginald was duelling for revenges so some of people called him the revenger.
shark is duelling but if his opponent lose he takes his deck he was duelling with bronk and bronk lose the duel and his deck.
then Yuma came he was the friend of bronk and he wanted shark to return bronk's deck back but shark took away the golden key that hi parents gaved to Yuma and broke it under his foot so Yuma and shark duelled but in the midst shark activates a strange trap card then told Yuma that he will lose but Yuma told shark about his father and his advice that always to feel the flow and Yuma says I do so and takes of the remaining part of his key then he found him self to the strange in his dream but it was real and he looked at his key hefound it fine and unbroken he was able to open the door but he found himself ina dark place sitting on the breze and 99 cards surrounding him but he return back to the duel and found some one called astral he was different but astral told him that the99cards affect its owner and he needs to collects these99cards also to have his memory back Yuma can seehim but others no astral listens to the word duel he remembered his duelling skills and he helped Yuma to duel however shark was affected by a number card that is number 17 and that card was leviathan dragon yuma sacred but he duelled and he was overlating monsters but astral gave him the only number card that he has that was number 39 utopia and by astral he won the duel against shark then he return him the deck and goes.
later Yuma wants to duel shark again but if he lose he would give him his golden key however shark wins without taking any damage and he takes his key then he return it to Yuma again and telling him keep it as a remainder to what I did to you and tells him do not get involved with me
