Taishi Miwa is a close childhood friend and confidant of Toshiki Kai, attending the same school. He exhibits a carefree, joking personality contrasting Kai's reserve, while showing genuine concern for friends, and possesses a yellow Vanguard circle. Miwa remained in Japan managing Card Capital with Izaki while others competed in tournaments, later advancing to senior status alongside Kai. He participated in regional qualifiers, defeating Shingo but losing to Misaki using a Seal Dragon deck. After Kai returned affected by Reverse, Miwa deduced his involvement in spreading it and confronted him. Using a Kagero deck featuring Dragonic Overlord the End, he lost to Kai's Chaos Breaker Dragon and became Reversed. As Kai's subordinate, he overpowered underground fighters and Jun to protect Kai's plans. Later, fighting Misaki at Tatsunagi Industries with Dauntless Dominate Dragon "Яeverse", he lost to her Omniscience Regalia, Minerva, reverting to normal and expressing sorrow over Kai's renewed isolation. Following Aichi Sendou's disappearance, Miwa lost memories of him. Seen with Kai in their school's vanguard club, Kai challenged him to a match. Kai's activation of Legion with Seeker, Thing Saver Dragon and Blaster Blade Seeker during their fight triggered Miwa's recollection of Aichi. Miwa mentioned plans to attend an elite university aided by Misaki's academics and later investigated a butler connected to Aichi. During "G Quest", Miwa reappeared as a Card Capital employee, referred to as the Sub-Sub-Manager by Misaki, and served as a guardian within Dragon Empire. His primary deck is Kagero, centered on empowering units through Garnet Dragon, "Flash" and retire tactics using cards like Berserk Dragon and Chain-attack Sutherland. He uniquely favors the obsolete Lizard Soldier, Undeux. The manga alternatively depicts him using a Nova Grappler deck focused on resting and standing rearguards, combining Boomerang Thrower and Cat Butler for multiple attacks supported by Miss Splendor to bypass interception. Miwa is typically seen wearing his Hitsue High School uniform, a blue-trimmed white jacket and pants, with a pink hoodie underneath. Though his given name is Taishi, characters consistently refer to him by his surname, Miwa, adhering to Japanese etiquette norms reflecting perceived social distance, including from Kai.