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Tsuboi Ryoutarou (壷井遼太郎, Tsuboi Ryōtarō?)[3][4], known as Klein (クライン, Kurain?) 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.[5] 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[6], but he has brownish[citation needed] 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.[6] 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[]

Klein's ALO avatar

Klein's ALO 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.


Originally, Klein was a new player who identified Kirito as a beta tester, and requested help from him. After learning the basics of the game from Kirito and learning that Sword Art Online had become a death game, Klein rejoined his friends in order to assist them, and later formed a guild with them. He was a stern supporter of Kirito, despite the general opinions of beta testers.[5]


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.[citation needed]

Klein is a very loyal person, which is apparent in his friendship with Kirito, despite the latter usually treating him with coldness.[citation needed] 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.


Aincrad Arc[]

November 6, 2022[]


Klein using the skill Reaver.

On November 6, 2022, Ryoutarou and his friends acquired a copy of Sword Art Online and were featured on the news as one of only 10,000 people who managed to purchase the game. Soon after logging into the game following its official launch, Klein 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, Klein 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.


Klein and Kirito part ways

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.

Red-nosed Reindeer[]

A few days before Christmas, Klein and Kirito 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.

The Progressors[]

At the beginning of March, Klein and the other Clearers spent a week in an effort to circumvent the GeoCrawler, the Field Boss of the 56th Floor that was blocking the path to the local Labyrinth, as frontal attacks against it were ineffective, while its position prevented flanking the monster. On March 6, 2024, Klein and Kirito attempted to bait the GeoCrawler with an A-class meat; however, they were forced to quickly retreat to the local village, barely managing to close the gate behind them before the boss could enter.

When Asuna entered into a dispute with Kirito later that day regarding whether or not Non-Player Characters (NPCs) should be used to distract the GeoCrawler, Klein interrupted to inquire on the vice commander's level. Upon Asuna disclosing her current level, the man declared that while his own level was significantly lower than hers, Kirito had reached one level higher than her. To Klein's surprise, this provocation resulted in the boy being challenged to a first-strike duel, prompting Klein to apologize to Kirito for inadvertently forcing him into the predicament.

The day after Kirito's victory in the duel, on March 7, the Clearers learnt that a lullaby could lull the GeoCrawler to sleep. Upon successfully utilizing this piece of intelligence to incapacitate the monster, Klein and the rest of the vanguard party climbed over its back and attacked its weak point from behind until the monster was defeated.

August, 2024[]

Klein was one of the members of the crusade against Laughing Coffin.

October, 2024[]

On October 18, 2024, Klein and his guild encountered Asuna and Kirito in a safe zone in the Labyrinth of the 74th Floor. Their meeting was interrupted by an Aincrad Liberation Force (The Army) platoon, whose leader 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 encountered 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.

November, 2024[]

On November 7, 2024, Klein participated in the 75th Floor boss battle against «The Skull Reaper». As Heathcliff's identity was uncovered in the aftermath of the battle, Klein and the other Clearers, excluding Kirito, were paralyzed by the mastermind of the death game in order for him to have a duel with Kirito. Before the duel, when the black swordsman apologised to Klein for leaving him on the first day, Klein shouted that he would only forgive the boy if he bought him a meal in the real world as compensation.

Fairy Dance Arc[]

Ryoutarou 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[]

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

Rainbow Bridge[]

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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».


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.

Alicization Arc[]

Alicization Exploding[]

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Alicization Awakening[]

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Alicization Lasting[]

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Sword Art Online[]

Stat Value Time
Level 59
December 19, 2023[8]
End of game

Known Equipment[]

Sword Art Online[]

Name Type Acquisition Notes
«Karakurenai»[† 2] Katana


Sword Art Online[]

One Handed Curved Blade Katana Light Metal Equipment Lightweight Shield Equipment Battle Healing
957 / 1000
822 / 1000
933 / 1000
861 / 1000
562 / 1000
First Aid Searching Straining Extended Weight Limit Fighting Spirit (Hate Skill)
759 / 1000
710 / 1000
594 / 1000
685 / 1000
712 / 1000
366 / 1000

Sword Skills[]

One Handed Curved Blade[]

ALfheim Online[]

Sword Skills[]



See Tsuboi Ryoutarou/Image Gallery


  • Ryoutarou was one of the hardcore gamers who were waiting for three days in line during the SAO release.[9]
  • The author chose to name Ryoutarou's avatar as "Klein" based on an American bicycle company named Klein Bikes.[10]
  • In-story, Ryoutarou's avatar name was derived from the term Klein bottle (クラインの壺, Kurain no Tsubo?), based on his real name Tsuboi Ryoutarou.[4]
  • Klein was one of the 10+ players who had the «Katana» extra skill.[11]
  • In the 4-koma manga parody of Sword Art Online, Klein is much more prominent and he tends to pester 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.[12]
  • Klein nicknames Kirito as Kiri-no-ji (キリの字?).


  1. This entry is based on a tentative list by the author that has neither been confirmed nor denied as final.
  2. However, in the 'face to face' Q&A page about Klein that come together with a popularity vote, he was said to be using Kokuenmaru as his last Katana in SAO



Major Characters
Alice Zuberg - Asada Shino (Sinon) - Ayano Keiko (Silica) - Eugeo - Kayaba Akihiko - Kikuoka Seijirou - Kirigaya Kazuto (Kirito) - Kirigaya Suguha (Leafa) - Shinozaki Rika (Lisbeth) - Tsuboi Ryoutarou (Klein) - Yui - Yuuki Asuna (Asuna)
SAO Players
Aincrad Liberation Force/ALS Hokkaiikura - Joe - Kibaou - Kobatz - Liten - Melonmask - Okotan - Schinkenspeck - Thinker - Yulier - Yakumo
Divine Dragon Alliance/DKB Buxum - Hafner - Lind - Morte - Schmitt - Shivata - Yamata
Fuumaningun Isuke - Kotaru
Fuurinkazan Dale - Dynamm - Harry One - Issin - Klein - Kunimttz
Golden Apple Caynz - Grimlock - Griselda - Schmitt - Yolko
Knights of the Blood Asuna - Daizen - Godfree - Heathcliff - Kirito - Kuradeel - Nautilus
Laughing Coffin Johnny Black - Kuradeel - Kuro - PoH - XaXa
Legend Braves Beowulf - Cu Chulainn - Enkidu - Gilgamesh - Nezha - Orlando
Moonlit Black Cats Ducker - Keita - Kirito - Sachi - Sasamaru - Tetsuo
Titan's Hand Rosalia
Two-Handed Builders Agil - Lowbacca - Naijan - Wolfgang
Others Argo - Ashley - Ceba - Coper - Diavel - Gin - Gwen - Kein - Lisbeth - Lux - Mina - Mito - Nishida - Rossa - Ryufior - Sasha - Silica - Yuna
Beta Testers Argo - Coper - Diavel - Isuke - Kirito - Kotaru - Mito - Morte
NPC Angel - Kizmel - Leyshren Zed Yofilis - Lion - Myia - NPC Orchestra - Pina - Ruru - Scarecrow - Theano - Tilnel - Tin - Toto - Yui
Non-Canon Aaaa - Ado - Alberich - Alice Zuberg - Amiira - Ceniza - Clumy - Cocoa - D.I.L - Eugeo - Fer - Fuego - Garcia - Idhrendis - Inas - Knakia - Koharu - Lapis - Leafa - Leuer - Linhua - Mariah - Mater - Mikiha - Miyurin - Notte - Oculus - Philia - Protagonist (Integral Factor) - Rain - Rano - Sanya - Seeda - Sinon - Stilla - Strea - Typhon - Ulrik - Vela - Vecta - Wendelin - Yuuki
ALO Players
Cait Sith Adie - Alicia Rue - Silica - Sinon
Gnome Agil - Tecchi
Imp Yuuki
Leprechaun Ceba - Granze - Lisbeth - Talken
Pooka Sasha
Salamander Eugene - fastuosa - Gtacs - Jun - Kagemune - Klein - Mortimer - UxperXJ
Spriggan Kirito - Kuro - Nori
Sylph Erika - Fukaziroh - Leafa - Lux - Recon - Sakuya - Sigurd
Undine Asuna - Chrysheight - Siune - Thinker - Yulier
NPC/Navigation Pixie Angel - Emely - Hraesvelg - Leviathan - Nerakk - NPC Orchestra - Pina - Skuld - Thiazi - Thor - Thrym - Tonky - Urðr - Verðandi - Yui
Others/Unknown Ashley - Fairy King Oberon - Garnet - Gwen - Marinca - Saitou Shouichi - Slug Researchers
Non-Canon Alice Zuberg - Argo - Black Lotus - Eugeo - Heathcliff - Persona Vabel - Philia - Rain - Sachi - Seven - Strea - Sumeragi - Yuna
GGO Players
Dyne's Squadron Arashi - Dyne - Ginrou - Jin - Miso - Sinon
BoB Participants Blackwood - Colonel Liberty - DA*LU - Dyne - E.J. - Fernil - Garrett - huuka - Jack Reacher - JIGEN - Kakouton - kaeeeede - Kakameposu the II - Keith - Kirito - Lion King Richie - Masaya - Musketeer X - No-No - Pale Rider - Pancho - Raiden - Licoco - Setsugekka - Shishigane - Sinon - Sterben - Stinger - Subtilizer - Ten-Q - Uemaru - Usujio Tarako - Yamikaze - XeXeeD - XYZ
Death Gun Victims Garrett - Pale Rider - Usujio Tarako - XeXeeD
Squad Jam Participants KKHC Shirley
LPFM Fukaziroh - LLENN - M - Pitohui
MMTM Bold - David - Jake - Kenta - Lax - Summon
Narrow Dashin - Hidehide - Nagama - Nobu - Saika - Yasu
SHINC Anna - Eva - Rosa - Sophie - Tanya - Tohma
ZAT Benjamin - Casa - Frost - Koenig - Yamada - Let's Play Host
ZEMAL Heuy - Max - Peter - Shinohara - Tomtom
Others Clarence
Other main series characters Behemoth - Spiegel
AGGO manga original characters Batian - Boss - Costa - Lorosae - Panama - Rio
Non-Canon Afasys - Agil - Alice Zuberg - Argo - Asuna - Bazalt Joe - Daisy - Eiji - Eugeo - Itsuki - Klein - Kureha - Leafa - Lievre - Lisbeth - Philia - Premiere - Protagonist (Fatal Bullet) - Rain - Sachi - Seven - Silica - Strea - Yui - YUNA - Yuuki - Zeliska
Underworld Resident
Human Empire Rulid Village Algu - Alice Zuberg - Bercouli - Donetti - Doyke - Eugeo - Garitta - Gasupht Zuberg - Ivenda - Jaina - Jink - Kirito - Nigel Balbossa - Orick - Ridack - Sadina Zuberg - Selka Zuberg - Sister Azalia - Sulinea
Zakkaria Banou Wolde - Egome Zakkarite - Kelgam Zakkarite - Telin Wolde - Telulu Wolde - Toriza Wolde
Centoria Azurica - Cardinal - Quinella - Sadore - Yazen
Sword Mastery Academy Azurica - Eugeo - Frenica Szeski - Golgorosso Balto - Humbert Zizek - Kirito - Raios Antinous - Ronye Arabel - Sortiliena Serlut - Tiese Shtolienen - Volo Levantein - Zobun
Central Cathedral Ayuha Furia - Berche - Cardinal - Charlotte - Chudelkin - Elevating Operator - Fizel - Hainag - Hana - Linel - Quinella - Soness Furia - Xiao Choucas
Integrity Knight Alice Zuberg - Bercouli - Dakira - Deusolbert - Eldrie Woolsburg - Entokia - Eugeo - Fanatio - Fizel - Giro - Hobren - Jeis - Linel - Nergius - Renly - Scheta
Dragons Amayori - Himawari - Hinageshi - Hoshigami - Kazenui - Shimosaki - Takiguri - Tsukigake - Yoiyobi
Others Alderes Wesdarath V - Almera Woolsburg - Cruiga Norlangarth VI - Eolyne Herlentz - Eschdol Woolsburg - Hozaika Eastavarieth - Zeppos
Dark Territory Black Iums D.I.L - Dampe - Fu Za - Iskahn - K.U.V - Leazetta - Lengil Gira Scobo - Lipia Zancale - Vixur Ul Shasta - Yotte
Orcs Moricca - Renju - Rilpirin
Ogres Furgr
Giants Sigurosig
Goblins Aburi - Hagashi - Kosogi - Kubiri - Oroi - Shibori - Ugachi
Non-Canon Aleo - Cardo - Carver - Dorothy Isaiah Elisheva - Edith - Elcar Marscull - Fazahd - Hektor Ul Günther - Hersyrian - Jared - Kainan - Kayode Norlangarth - Kirimai - Lushe - Mary - Medieta - Medina Orthinanos - Momento - Paulie Aurimas - Phinea Suvale - Proxy - Rogu - Round Robin - Sarai - Shirley - Somelier - Sylvie - Tolgash Southacroith III - Vallenthor - Wegin Sorby - Zacza - Zappas - Ziczi
Underworld Visitors
Agil - Alicia Rue - Asuna - Eiji - Eugene - Gabriel Miller - Hirono Takashi - Jun - Kirito - Klein - Leafa - Lisbeth - Moonphase - Nori - Sakuya - Silica - Sinon - Siune - Tecchi - Vassago - YUNA
Non-Canon Argo - Ceba - Itsuki - Kureha - Mito - Philia - Premiere - Rain - ReoNa - Seven - Strea - Tia - Yui - Yuuki - Zeliska
Asuka Empire
Players Clevel - Koyomi - Merida - Nayuta - Ran - Yanagi - Yuuki
NPC Clovis (AI)
Staff Torao
Reality/Other Games
Rath Aki Natsuki - Higa Takeru - Hiraki - Ichiemom - Kikuoka Seijirou - Koujiro Rinko - Nakanishi - Niemom - Yanai
Others Alicia Klingerman - Cel - Clovis - Critter - Doctor Kurahashi - Eiji - Endou - Fujita Shin - Kirigaya Midori - Kirigaya Minetaka - Okano Kouji - Oosawa Mizue - Oosawa Sachie - Sada Akiyo - Satou Rei - Shigemura Tetsuhiro - Yuna - Yuuki Kouichirou - Yuuki Kyouko - Yuuki Shouzou
Non-Canon Es - Gattas - Genesis - Goliath - Kaede - Laraiah - Layla - Michael - PoH (Variant Showdown) - Premiere - Richter - Sigil - Teria - Tia