Tsuboi Ryoutarou

Tsuboi Ryoutarou (壷井遼太郎), known as Klein (クライン) 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. Klein 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.

Real Life / Sword Art Online Avatar
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.

ALfheim Online Avatar


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.

Background
Originally, Klein was a new player who identified Kirito as a beta tester, and requested help from him. Kirito trained him in the basics of Sword Art Online and was impressed with his progress. Klein later rejoined his friends in order to form a guild. He was a stern supporter of Kirito, despite the general opinions of beta testers.

Personality
Klein is one of the friendliest people in the series and sets the mood when he's 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. He is very loyal to Kirito, despite Kirito usually treating him with coldness. It is later revealed this coldness is due to Kirito feeling guilty for leaving Klein behind at the beginning of Sword Art Online. Klein does not care about this and the two make up as Klein is shown to be the person Kirito relies on the most, beside Asuna.

Klein is also a "bachelor" and is shown trying to get together with various women in the series, such as Asuna, Freyja, and even Kirito's sister, who he had yet to meet. He usually has no luck, however, making him somewhat of a comic relief.

Aincrad Arc


He was first seen posing with his friends while a female news reporter was reporting about Sword Art Online and how only 10,000 copies were sold. Early in the official version of the game, he noticed and identified Kirito as a beta tester, and asked to be taught the basics of fighting. Soon after understanding the basics, he attempted to log out so that he could eat his pizza, but noticed that there was no log out option.

Afterwards, he and Kirito were recalled to the Town of Beginnings, where Kayaba Akihiko announced that Sword Art Online had become a death game and a reality. Shortly afterwards, the avatars of players, including Klein's, were transformed to look like the real bodies of the players.



After the tutorial, Kirito took him to the streets of the city, telling him that they needed to get to the next village together. But Klein refused the offer by saying that his friends must be in the plaza and that he needed to be with them. He suggested that they could all go together, but noticed that Kirito felt worried about the idea, so he dismissed it. Soon they parted ways, with Kirito heading to the next village and Klein returning to the plaza.

They met each other by chance on various occasions throughout the two years in Aincrad due to both of them being in the front lines later on in the game. The first of such known encounters was when Kirito went to the Wolf Plains to do some overnight leveling, as he spent most of the day helping his Guild, the members of the Moonlit Black Cats level up at a fast rate. Another meeting was a few days before Christmas, when they met at the Ant Hill on the 46th Floor, which was the most efficient leveling area at the time. Then again during Christmas, when he tried to convince Kirito not to battle Nicholas The Renegade alone, but Klein eventually let Kirito go while he and his guild kept the Divine Dragon Alliance from taking on the boss. When Kirito came back, he gave the revival item to Klein, telling him that to use it on the first person he saw dying. In August 2024, Klein was one of the members of the crusade against Laughing Coffin.

Klein and Kirito later met up on the 74th Floor, when Klein and his guild encountered Kirito and Asuna in a safe zone in the Labyrinth. Their meeting was interrupted by an Army platoon who demanded a map of the Labyrinth. After the platoon departed, Klein, Kirito, Asuna and members of the Fuurinkazan decided to follow the platoon in case they got themselves into trouble. After seeing that the platoon had engaged with «The Gleam Eyes» and that crystals could not be used within the boss room, Klein and his guild helped get The Army members to safety.

Klein later met up with Kirito and Asuna on the 75th Floor for the boss battle, and they fought against «The Skull Reaper». After the battle, Heathcliff's identity was uncovered by Kirito and Heathcliff paralyzed all the clearers, except Kirito. Before Kirito began his duel with Heathcliff, he apologised to Klein for leaving him on the first day. In response to that, Klein told him that he would not forgive him for it until Kirito bought him a meal in the real world to make up for it.

Fairy Dance Arc
Klein was present at Andrew Gilbert Mills's Dicey Cafe to celebrate the «Aincrad Capture Commemorative Party», and was later also present during the unveiling of a content update in ALfheim Online, the «Floating Castle Aincrad», which introduced «New Aincrad» to the ALO universe.

Extra Edition
Klein joined Kirito and the others in the «Deep Sea Plunderers» quest in ALO.

Phantom Bullet Arc
On December 13, 2025, before the Bullet of Bullets tournament had begun, Klein, along with Asuna, Leafa, Lisbeth, and Silica, went to the fields to fight some monsters. While engaging a giant lizard in battle, Klein grabbed its tail but was assailed by the monster's poison breath. As Asuna was unresponsive, Klein had to call her several times before he was healed.

Klein was seen watching Kirito's battle during the Bullet of Bullets tournament at Asuna's rented house in Yggdrasil City. Upon seeing «Death Gun», he reacted by saying he knew the person from SAO as one of the members of the red guild, «Laughing Coffin».

Calibur
Klein was one of the players invited to join Kirito's party in an attempt to clear the Inverted Ice Pyramid. During the adventure, Klein helped Kirito obtain the Holy Sword Excalibur by setting Freyja, who was later revealed to be Thor, free. Thor rewarded him with Mjölnir for his assistance, which he then gave to Lisbeth as he did not use blunt weapons. Later when Skuld appeared at the end of the quest, Klein asked for her address.

Mother's Rosario
Klein accompanied Kirito to help Asuna in the Labyrinth on New Aincrad's 27th Floor. Together they managed to help stall a guild for three minutes in order to allow Asuna and the Sleeping Knights to fight that floor's boss. Several days after the boss battle, Klein participated in a barbecue party hosted at Asuna and Kirito's Forest House, which ended in an impromptu boss raid on the 28th Floor. Several months later, Klein was one of the thousands of players who came bid their final farewells to Yuuki in ALfheim Online. Some time later, Ryoutarou participated in a picnic with his friends in the real world.

Ordinal Scale
One evening, Ryoutarou and his guild participated in a battle against Kagachi the Samurai Lord in Ordinal Scale. The following evening, Ryoutarou and his guild, except for one member, gathered at a park for another boss battle. While the guild was waiting for the missing member outside of the appointed battlefield, another boss appeared right beside them. Although the guild was managing well against the monster, they were suddenly attacked by Eiji. Seeing Eiji incapacitating his friends with his fists, Ryoutarou dropped his Augma and attempted to retaliate. However, after a few unsuccessful attacks, Ryoutarou had his arm broken by Eiji, who then put the Augma back on him before offering him to the boss monster. The moment his hit points reached zero due to the boss's attack, the Augma stole his memories of Sword Art Online. In the aftermath, Ryoutarou was admitted to a hospital to treat his injuries.

Sometime later, Klein helped defeat «An Incarnation of the Radius» to help save the lives of the Sword Art Online survivors trapped by Shigemura Tetsuhiro.

One Handed Curved Blade

 * Reaver

Katana

 * Tsujikaze

Gallery

 * See Tsuboi Ryoutarou/Image Gallery

Trivia

 * Ryoutarou was one of the hardcore gamers who were waiting for 3 days in line during the SAO release.
 * Ryoutarou's avatar name, Klein, was derived from the term Klein bottle (クラインの壺い), based on his real name Tsuboi Ryoutarou.
 * Klein was one of the 10+ players who had the extra skill «Katana».
 * In the 4-koma Klein is much more prominent and he tends to bug Kirito with messages or calls.
 * In all commercially released media Klein first met Kirito on the first day of the SAO official service start, but in the web version, Klein first met Kirito on September, 2013 (2023 in the light novel timeline), three months before the Christmas Event.
 * Klein nicknames Kirito as Kiri-no-ji (キリの字).

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