Bastion Misawa, known as in the original Japanese language version, is a fictional character in the Yu-Gi-Oh! GX anime and manga series. In the English version, Bastion is voiced by Eric Stuart, while Yūki Masuda takes the role in the Japanese version.
A highly analytic duelist, Bastion is portrayed as a mathematical genius who covers his cards and the walls of his room with endless numeric formulas, believing that everything in life can be calculated arithmetically. The neglect of his character is a running gag throughout the series.
Upon defeating Chazz Princeton in a public Duel, Bastion is offered entrance into Obelisk Blue, but declines, saying he promised himself he would not advance to Obelisk Blue until he was the #1 freshman of the school, and in order to do so, would have to defeat Jaden, who he viewed as #1. He builds a seventh deck, seemingly based on his Water deck, devoted to sealing certain cards so that an opponent will not be able to summon most of his or her monsters. Bastion uses the seventh deck against Jaden, preventing the use of Polymerization with Cursed Seal of the Forbidden Spell, therefore keeping Jaden from calling forth his stronger monsters, but is still defeated.
Due to his skill, Bastion is one of the seven duelists that received a key to the Spirit Gate that can unleash the Sacred Beast Cards. Bastion only duels one of the Shadow Riders, Tania. Although Bastion uses his Magnet monsters, which use opposing plus and minus charges to stop his opponent's attacks and fuse to become stronger, he eventually loses. Afterwards, he is stripped of his free will to a degree and becomes infatuated with Tania, but returns to normal after Jaden defeats her in a Duel.
At one point during the second year, angered by the fact that he was not considered for entry into the Society of Light, Bastion challenges Sartorius to a Duel in order to prove his strength and disband the Society. Chazz, however, takes Sartorius' place, and although Bastion has the means of being victorious, Sartorius takes advantage of his self-doubt and desire to be accepted, convincing him to intentionally lose to Chazz and finally join the organization. This was his only duel shown in season 2.
Following his conversion, Bastion is relegated to the sidelines, watching helplessly as other Society members are given the opportunity to duel Jaden and convert other school members into their group, while he himself is assigned no such tasks. After weeks of such torture, as well as a conversation with Dr. Eisenstein, he grows "enlightened" about his worth as a duelist and as a person, strips himself of his clothes and leaves the Society of his own accord to pursue his goals, running through the school in Archimedes-inspired fashion. This occurs in episode 96, in the 4Kids dub, he is not fully naked and wears boxers unlike the original japanese version. He follows Eisenstein to his laboratory, where the two study quantum mechanics together, but an experiment deposits Bastion in an alternate dimension where the rest of Duel Academy would later join him. Prior to Jaden's duel with Yubel, Bastion decides to stay in the alternate dimension with Tanya and her friends.
Despite his protests that such feelings are illogical and irrational, it is implied that Bastion has feelings for several female Monster Cards seen throughout the series (his primary crush being White Magician Pikeru). In the English version, Bastion speaks with a British accent.