Isao Kachidoki

Isao Kachidoki ( Kachidoki Isao) is a character in the Yu-Gi-Oh! ARC-V anime. He is participant in the "Junior Youth" class of the Maiami Championship and is the ace of the Ryozanpaku School.

Personality
As a child, Isao seems timid and like child his age, Dueling because he thought it's fun, and was initially seemed reluctant to join Ryozanpaku whose Dueling believing is absolute victory. However, the harsh training he received at Ryozanpaku for years has completely changed him into a very violent person, repeatedly physically assaulting his opponent during Action Duels to prevent them from getting cards in order to win at any cost. Like other Ryozanpaku Duelists, he thinks that Dueling is a serious battle and not for fun as Yūya believes to be.

Past
Eight years before the story, as a child, Isao was given a Duel Disk by his parents and was admitted into Ryozanpaku Duel School. One day, on the day he departed to the school, he was seen walking with Ryōzan Gōdagawa, until he stopped and noticed a young Yūya Sakaki Dueling with his father, Yūshō Sakaki, which left a deep impression in his heart. Seeing them having fun in their Duel caused him to smile, but his teacher told him not to think of Dueling as fun, as the path he was about to walk would be pitch black and full of darkness.

At one point in his life, Isao had gotten second place in the previous Maiami Junior Youth Championship. According to Nico Smiley, Isao further evolved from the previous tournament by learning Fusion Summon.

Round 1
During his Duel with Yaiba Tōdō, Isao brutally beat up Yaiba in order to prevent him from getting any Action Cards, thus resulting in Yaiba's defeat in an One Turn Kill.

Round 2
During his Duel with Yūya, Isao once again tried to prevent his opponent from getting Action Cards through brutal force. While it seemed like Isao would win, Yūya entered The Awakening, which allowed him to Xyz Summon "Dark Rebellion Xyz Dragon" and beat Isao in an One Turn Kill. This Duel exposed Isao's ignorance towards Xyz Monsters as he thought that since they have Ranks, it was implied that their Levels would be 0 and he could activate the effect of "Idaten the Conqueror Victory Star". When Yūya offered to help Isao up after the Duel, he disdainfully rejected it and bowed in shame to his master and the other Ryozanpaku Duelists.

Allying With Academia
After his loss, Isao was treated coldly by everyone in his school, which he commented as the same as being excommunicated, making him frustrated and humiliated. He started to trained himself more than before, but the training was not enough to appease his bitterness and felt he will stay stuck in his current state unless he is able to have a rematch and defeat Yūya. He was then approached by Dennis who told him that Yūya will eventually come to the Fusion Dimension, so he invited Isao to join him if he wants to defeat Yūya, which Isao agreed.

Rematch Against Yūya
When Yūya, Kaito, Shingo, and Gongenzaka arrived in the Fusion Dimension to save Yuzu from Academia, Dennis told Isao who was waiting inside the car that it's his turn. Getting out, he pinned down Yūya and challenged him for a rematch to avenge his previous loss. He started his turn by immediately Summoning his ace monster, "Idaten the Conqueror Victory Star". He then told Yūya to bring out "Dark Rebellion Xyz Dragon", resenting the monster that Yūya used to defeat him. Once Yūya did so and activated its effect, Isao activated "Kaiki the Sky Fusing Star"'s effect to summon it back from graveyard and then fused it with "Idaten" to Fusion Summon "Shura the Supremacy Star". Due to "Kaiki's" effect, the summoning came at the cost of receiving 500 damage to Isao's own LP for each of his Standby Phase. Despite the pain from the effect, Isao wasn't bothered by it and instead confident that the power of "Kaiki's" curse, will help him to defeat Yūya. Isao prevented Yūya from getting any Action Card by physically attacking him like before, and Yūya barely defended "Dark Rebellion" by using the Pendulum effects of his monsters to overcome the disadvantage due to using Xyz monster. In his second attempt to get an Action Card, Yūya successfully avoided Isao's attack and got one by using Allen's roller skates, slowly turning the tide. Isao tried to get an Action Card to counter, but couldn't to find any, driving him into desperation. Isao insisted that he won't accept another lost, having vowed to himself that he will defeat Yūya ever since he saw Yūya Dueling happily with his father eight years ago. In desperation, Isao tried to destroy both himself and Yūya by using his trap card, "Evil-Sealing Flash" that will destroyed all monsters affected by the card and inflicted 2000 damage to both players. The impact of the card destroyed the ground they were standing in the process, but Yūya saved both of them by activating "Acrobat Tower" to call back all of their monsters from graveyards, Isao was saved from the fall by "Idaten". Yūya challenged Isao to a gamble using his "Acrobat Tower", their victory or loss will be determined by how low the level of monsters they draw. Isao accepted the challenge, and unluckily drew two high level monsters, leading to his second defeat. Isao lamented over his second lost, but was interrupted when Yūya once again offered his hand to help him stand up while saying that he had fun Dueling against him. This time, Isao accepted Yūya's hand as he watched how the audience were impressed and clapping for their Duel. Before leaving, he admitted that Yūya's Entertainment Dueling is not as bad as he believed it to be, much to Yūya's happiness.

Deck
Isao uses a "Star" Deck focused on Fusion Summoning his ace monster, "Idaten the Conqueror Victory Star". During his Duels he shows a very violent style, physically assaulting his opponents with martial arts to prevent them from getting Action Cards. His core strategy is Fusion Summoning "Idaten", using its effect to reduce the ATK of his opponent's monsters with lower levels to 0, and equipping it with "Magical Star Sword", which can increase the ATK of the equipped monster by sending Magic Cards from the hand to the Graveyard. He then proceeds to gather Action Cards and use this effect to power up "Idaten" to the point where he can perform a One Turn Kill.

After his loss against Yūya, more precisely against "Dark Rebellion Xyz Dragon". Isao follow his strategy and adds "Kaiki the Sky Fusing Star" to counter "Dark Rebellion's" effect, and brings out "Shura the Supermacy Star". The effect of "Shura" reduces the ATK of all monsters on the field to 0, and give them 200 ATK times their Level in battle, effectively shutting Xyz Monster with no Level. Covering the weakness of "Idaten".