Kozuka is a Duelist, nicknamed "Ghost" for his use of ghost-like Duel Monsters cards. He took part in the Duelist Kingdom tournament, where he, Takaido[Note 1] and Satake[Note 1] teamed up with Bandit Keith, who helped them at first, before later turning on them. He also took part in the Battle City tournament, where he was defeated and killed by Dark Bakura.
Kozuka took part in the Duelist Kingdom tournament. Here he met up with, Takaido,[Note 1] Satake[Note 1] and Bandit Keith Howard. Keith was the former United States champion, but had not been invited to the tournament. He offered to help the Kozuka, Takaido and Satake earn forty Star Chips between them, so that the four of them could enter Pegasus Castle, as the semifinalists. With his help they had earned four, five and five Star Chips respectively, before Kozuka and Satake spotted a group of people, including Yugi Mutou, while searching for opponents. They informed Keith of their find, but thought they were better avoiding this group, as Yugi would be too difficult to defeat. However, Keith suggested that they separate the other Duelist from that group, Katsuya Jonouchi and force him to Duel in the hidden underground crypt. As the crypt had a Graveyard terrain, which strengthened undead cards, Keith suggested that Kozuka Duel, since his Deck was filled with Ghost cards. However, after looking through it, he said it would not suffice, so he lent Kozuka some of his own cards, to strengthen it. When Jonouchi left his friends to urinate in private, Kozuka, Takaido and Satake snuck up behind him, grabbed him and dragged him into the crypt. Kozuka imposed the wager of four Star Chips for the Duel.
Kozuka planned on Summoning a Ghost card, but was stopped by Keith, who over the next three turns, insisted that he play non-Ghost cards, which were all weaker than Jonouchi's monsters. Kozuka then drew "Call of the Haunted", which revived the destroyed monsters as Zombies, powered up by the Graveyard terrain and capable of resurrecting even stronger when beaten. When Kozuka was about to attack one turn, Keith suggested that he draw another card to try and power up the Zombies, even further first. Kozuka then got "Pumpking the King of Ghosts", which powered up his Zombies every turn. Jonouchi played safe, but putting his monsters in Defense Mode, but Kozuka eventually drew "Stop Defense". Jonouchi used "Red-Eyes Black Dragon" to destroy "Pumpking" and on his last turn, used "Shield and Sword", which switched the ATK and DEF of all monsters. The Zombies, which only attacked based on instinct, were incapable of defending and as such had 0 DEF, which became their new ATK. This gave Jonouchi an opening to damage Kozuka's Life Points and win the Duel.
After exiting the crypt, Keith then ordered Kozuka, Takaido and Satake to block the exit with a boulder, trapping Jonouchi, Yugi and their friends inside. They obeyed, but Kozuka wondered if they had went too far. Keith then moved on to his "next order of business" and proceeded to beat up Kozuka for losing, kicking him in the stomach. Kozuka pleaded that he had only played the cards Keith told him to, but Keith insisted that he should have won in that case and kicked him in the face. As Kozuka lay on the ground, Keith spat on him and commented that without his Star Chips, he was useless and should just die. Keith also took Takaido and Satake's Star Chips and beat them up, leaving the three lying on the ground in pain, while he went to Pegasus Castle alone.
"Ghost" Kozuka was one of the many Duelists who migrated to Domino City at the rumor of a new Duel Monsters tournament being announced by Seto Kaiba at Domino City Museum. The next day, Kozuka was present at the opening ceremony of the Battle City tournament, with the rest of the eligible Duelists.
During the actual tournament, he Dueled Dark Bakura shortly before the championship stages, but his Ghost Deck was easily overpowered by Dark Bakura's Occult Deck. Kozuka lost the Duel and his Puzzle Cards. As a Penalty Game, Dark Bakura took his life, using the Millennium Ring.
In the non-canon game Duel Links, Bonz is revealed to have survived Battle City and reappears as a playable character. However, his encounter with Bakura has left him frightened.
Kozuka used a Ghost Deck, during Duelist Kingdom. However Bandit Keith considered it insufficient for his Duel against Katsuya Jonouchi and lent him cards to make it more powerful. His new Deck contained a number of non-Ghost monsters, which he was able to revive through "Call of the Haunted", as near-unkillable Zombies. The Graveyard terrain and "Pumpking the King of Ghosts" made them stronger. The last part of the combo was "Stop Defense", to ensure the Zombies could damage the opponent's Life Points.
In Battle City, Kozuka still used a Ghost Deck. However, none of his cards were shown.Some use of "" in your query was not closed by a matching "".
Kozuka took part in the following Duels.
|VS — Katsuya Jonouchi||Duelist Kingdom||Lose||30, 31, 32|
|VS — Dark Bakura||Battle City||Lose||142|
- This name is not used in the manga.