Thunder, known in Japan as Ikazuchimaru (雷丸) is one of the four members of the Light Brigade led by Sarina. He and fellow member Frost were called upon by Sarina to battle Syrus Truesdale and Tyranno Hassleberry after they kidnapped Solomon Muto and baited them to the top of a large building in Domino City. Unlike Frost, he was more willing to use teamwork to win. He was given a copy of "Mirror of Duality" by Sarina, but could not use it since his Life Points were too low. However, Frost himself played the same card and won the Duel, with Thunder losing all his Life Points along with their opponents. He was sealed in a mirror by Sarina when she no longer had any use for him, but was freed alongside the other Light Brigade Duelists after Jaden Yuki and Aster Phoenix defeated her.
The "Ikazuchi" portion of his name in the Japanese version is derived from the word "ikazuchi" (雷), meaning "lightning".