Nagumo was a student at Domino High School with a knack for gaming—and scheming. He tried to capitalize on Monster Fighter's popularity by stealing equipment from classmates and reselling it at massively inflated prices (around 30,000 yen). When he approached Yugi to play, he seemed friendly enough until he revealed his real "house rule": loser hands over their gun and monster. Yugi was caught off guard, and Nagumo beat him down and took his monster, Alti.
Dark Yugi eventually tracked Nagumo down at the gym, where he'd been hawking Monster Fighter gear. The challenge that followed was no ordinary game—Dark Yugi warned him it would be a Shadow Game. Nagumo fought dirty, trying to punch his way through, but Dark Yugi's borrowed monster Killer Emaada knocked out Wild Spider in the first round. Since it was a Shadow Game, Nagumo felt his monster's pain physically, his face cracking under the impact. He cheated again in round two with a kick to Dark Yugi's side, winning that set, but Dark Yugi responded by ramping the shadow mode to level three. In the final round, Nagumo's own stolen monsters and Wild Spider pinned his legs down, and his monster was replaced by a twisted reflection of his soul. Dark Yugi dealt the finishing blow, and Nagumo went down hard.
Later, after a Duel where Nagumo won a "Diamond Dragon" card, he demanded his opponent sweeten the pot to match his card's value—100,000 yen. Kaiba Mokuba showed up and called him out for changing the ante rules and adding money to the wager. When Nagumo threatened him, Seto Kaiba himself arrived and made it clear that disrespecting Mokuba meant disrespecting Kaiba Corporation. Kaiba destroyed the card on the spot and challenged Nagumo to a Duel, staking a briefcase of rare cards and "The God of Obelisk." He even let Nagumo use the briefcase cards to compensate, though he planned to take them back after winning. The upgraded deck wasn't enough. Kaiba crushed him with Obelisk, took his Puzzle Card, and left Nagumo traumatized—screaming in terror as he watched the god card destroy him.
In the Duel Monsters anime, Nagumo was reduced to a one-off character, and his whole history with Dark Yugi was dropped.
Content compiled by AnimeList.moe from publicly available sources.
