Tsuboi Ryoutarou, known as Klein in «Sword Art Online» (SAO), «ALfheim Online» (ALO) and «Project Alicization», is a supporting character in the Aincrad Arc and a reoccurring character through the Sword Art Online series. He was one of the 10,000 players who were trapped in Sword Art Online, where he was the guild leader of «Fuurinkazan», one of the clearer guilds. After Sword Art Online was cleared, he began playing ALfheim Online as a Salamander. In both Sword Art Online and the real world, Klein wore a red bandana that held up his hair and was tied around his forehead. In Sword Art Online, he had spiky reddish hair, but he has brownish hair in the real world. He also had a hooked nose, a slight beard on his cheeks and chin, and, according to Kirito, he looked like a wandering samurai or a bandit. During the two years in Aincrad he used red robes and black armor resembling those of a samurai including a katana, along with his guild members. In ALfheim Online, Klein's appearance is mostly the same as his appearance in Sword Art Online, except that his hair is dyed red in ALfheim Online. Klein is one of the friendliest people in the series and sets the mood when he is around. He never holds grudges against others and is always ready to lend a helping hand. He cares deeply for his friends and always wants to be by their side fighting alongside them when they are in danger even to the point of getting angry when Kirito was fighting Death Gun, saying he should have converted to Gun Gale Online as well. He gets angry when people get into situations that can get them killed since he wants to protect as many people as he can. Klein is a very loyal person, which is apparent in his friendship with Kirito, despite the latter usually treating him with coldness. Klein is also a "bachelor" and is shown trying to get together with various women in the series, such as Asuna, Freyja, and even Kazuto's sister, whom he had yet to meet.