Harrington Rosewood, known in Japan as Mitsuru Ayanokouji (綾小路 ミツル, Ayanokōji Mitsuru), is an Obelisk Blue student, who is head of Duel Academy's tennis team as well as the heir to Ayanokōji Motors. He fell in love with Alexis Rhodes at first sight and desires to date her, much to the jealousy of Jasmine and Mindy. After seeing Alexis being friendly with Jaden Yuki, he grows jealous and duels Jaden over who becomes Alexis' fiancee. He loses the Duel. In the dub he vows to always love Alexis while watching the sunset. In the original Japanese, he yells that he hates Dueling.
Harrington uses a Tennis Deck, which largely includes "Ace" cards that inflict effect damage to his opponents, and "Ball" monsters like "Mystical Shine Ball" and "Mega Thunderball". His signature card, "Deuce", causes the Duel to resemble a tennis match by restricting the amount of times an opponent can attack, and giving the victory to the first Duelist to inflict damage twice.