Haga was the Japan regional champion, defeating Dinosaur Ryuzaki in the finals. His deck is based on Bug-Type monsters.
He entered Pegasus J. Crawford's Duelist Kingdom tournament. In his first interaction with Yugi Muto, he acted very polite and friendly in order to gain his trust and was given his Sealed cards. He then immediately threw the cards over the edge of the boat into the sea to prevent him from using them. (This pretense of politeness is much more believable in the original Japanese version than in the dub, when he sounds downright sarcastic and untrustworthy). Katsuya Jonouchi was only able to recover two of them. Yugi immediately decided to duel Haga first, risking his one Star Chip as well as his deck against Haga's two Star Chips. (In the manga, Yugi bets his life.) Yugi defeated Haga when he destroyed his Great Moth with his Demon's Summon, and the Japan regional champion was eliminated from the tournament and kicked off the island. Jonouchi took his dueling glove.
Haga entered Kaiba's Battle City tournament in Season 2, with a new card, Insect Queen, more powerful than his Great Moth. He promised a kid a rare card if he put a parasite card in Jonouchi's deck, but double-crossed him and sprayed him with arachno slime. Jonouchi dueled him, believing that he had stolen the kid's cards, and was unaware that the kid was working for him until he discovered the parasite card, which turned all his monsters into insects and prevented them from attacking (due to his Insect-Repellent Barrier), but his metal warrior was unaffected, and Jonouchi defeated Haga, taking his two Locator Cards and kicking him out of the tournament.
Waking the Dragons
In Season 4, Waking the Dragons, Haga and Ryuzaki attempted to steal Yugi and Jonouchi's rare cards, but were challenged to a duel by Grerimo, who beat them and took their souls. They were released after Yugi defeated Grerimo. Haga and Ryuzaki snuck aboard during Yugi's trip over to Pegasus' castle in the hopes of finding rare cards, and tried to get an Orichalcos card from Rafael, and became two of Dartz's henchmen after hitchhiking aboard Rafael's helicopter. Haga dueled Yami Yugi on top of a train, where he crossed the Moral Event Horizon by tearing up a card and claiming that Yugi's soul had been trapped inside it (thereby killing him), then sadistically revealed that he had been "joking"; the card was a merely a common Insect monster card. Enraged, Yami eventually defeated him by overkill. His soul was taken by the Orichalcos, and was released when Dartz and the Orichalcos God were defeated.
In the first half of Season 5, Grand Championship, Haga and Ryuzaki entered Kaiba's tournament as one duelist, and dueled Siegfried von Schroider, who easily defeated them with his Valkyries.
Dawn of the Duel
In the second half of Season 5, Dawn of the Duel, Haga and Ryuzaki stole Yugi's Millennium Items and Egyptian God Cards (only going after the latter), but ran into Yami Bakura, who temporarily trapped their souls in the Shadow Realm and returned the cards and items to Yugi. They suffered a lot of the consequences of Zorc ravaging the past, but survived it all.