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Klein, a close companion of the protagonist Kirito, is voiced by Hiroaki Hirata in the Sword Art Online anime series. Hirata is a renowned voice actor known for his roles in various anime, including Attack on Titan, Naruto, and Fullmetal Alchemist. Klein's character is characterized by his loyalty, bravery, and unwavering support for Kirito throughout their adventures in the virtual world of Aincrad.