Ryuji Maruyama
Ryuji Maruyama Omniverse.png
General Information
Species Human
Age 12 (Ben 10)
13 (Ben 10: Omniverse)
17 (Ben 10: Alien Force)
18 (Ben 10: Ultimate Alien and Ben 10: Omniverse)
Affiliations Killer Skull Gang
Occupation(s) Student
Juvenile Delinquent (formerly)
Apprentice Swordsman
Powers and abilities
Abilities Kenjutsu
Expert Martial Artist
Equipment Ryuji Maruyama's Katana
Voice Actor Charlie Schlatter (Ben 10)
Dante Basco (Ben 10: Alien Force, Ben 10: Ultimate Alien and Ben 10: Omniverse)
First Appearance Ben 4 Good Buddy

Ryuji Maruyama


Ryuji in the original series.

Ryuji's AF/UA Appearance

Ryuji has medium-length black hair, which covers the right part of his face. His eyes are dark brown, and the right one is always obscured by his hair. In Alien Force, his hair is quite longer than before, almost reaching down to his shoulders. In Omniverse, he has his hair cut short, now revealing both of his eyes.

In Ben 10, he wore a short black high-collared overcoat over a dark red shirt with elbow-length sleeves, calf-length dark blue pants, a black belt around his waist, white socks and red and black sport shoes. He also had a black wristband on his left wrist.

In Ben 10: Alien Force and Ben 10: Ultimate Alien, he now wears a black unbuttoned gakuran jacket with a red armband on the left sleeve over a unbuttoned white dress shirt with a dark red shirt underneath, black gakuran pants, red sneakers and a silver circle necklace. He still wears his black belt.

In Ben 10: Omniverse, he now wears a black leather jacket over a dark red shirt, dark blue rolled-up pants, a black choker, and black knee-high boots. He still wears his black belt and silver circle necklace. He also wears the black wristband he wore when he was 12, now in his right wrist instead of his left.


Ryuji is usually a criminally insane sociopath, willing to hurt/kill anyone for his own personal gain and/or pleasure, who is always bullying Shiori.

Ryuji also seems to be visibly annoyed by Rook's naivety and lack of experience on earth.

Powers and Abilities

Being an ordinary human, Ryuji has no powers, but he is a very skilled swordsman.


  • Ryuji shares several similarities with Kevin:
    • Both have black hair and dark brown eyes (although Kevin's eye color were not visible in Ben 10: Alien Force, Ben 10: Ultimate Alien and Ben 10: Omniverse)
    • Both fought Shiori Sakurai (Kevin always beated Shiori, while Ryuji was beaten by her)
    • Both were being hated by Shiori Sakurai and fought her, until they saved her (Kevin saved Shiori from being hit by a Highbreed, which led them to become fast friends, though they can still argue and tease each other sometimes, and Ryuji saved her from being attacked by Gwen Tennyson when she was controled by Diagon, which possibly led them to become interested on each other, though they can still argue and tease each other sometimes)
    • Both were introduced as sociopathic and insane characters, which led them to become antagonists, only to later on switch sides as the series progresses (Kevin in the first two episodes of Alien Force; Ryuji in the last two episodes of Ultimate Alien)

See also

Main Characters
Ben Tennyson | Gwen Tennyson | Izumi Kurokawa | Kevin Levin | Max Tennyson | Rook Blonko | Ryuji Maruyama | Shiki Sakurai | Shiori Sakurai
Supporting Characters
Julie Yamamoto | Manny Armstrong | Helen Wheels | Alan Albright | Jimmy Jones | Azmuth | Professor Paradox | Cooper Daniels | Ship | Eunice
Other allies
Plumbers (Tack, Vreedle Brothers (Octagon Vreedle, Rhomboid Vreedle), Magister Pyke, Magister Korwak, Magister Hulka, Joel Tennyson, Gordon Tennyson, Betty Jean Tennyson, Wes Green, Edward White, Mrs. Dalton, Mr. Hawkins) | Tetrax Shard | Gluto | Galactic Enforcers (Ultimos, Synaptak, Tini) | Reinrassic III | Myaxx | Xylene | Verdona Tennyson | Colonel Rozum | SATC (Lieutenant Steel) | Galvan (Retaliator) | Sugilite | Ignatius | Sandra Tennyson | Carl Tennyson | Frank Tennyson | Lili Tennyson | Technorg | Harvey Hackett | Hector | Elsgood | Sheriff Mason | Kai Green | Ishiyama | Camille Mann | Kiyoshi Sakurai
Former allies
Elena Validus | Phil | Squire
Deceased Supporting Characters and allies
Devin Levin | Magister Labrid | Magister Prior Gilhil |Pierce | Sir George | Winston | Victor Validus | Kwarrel | The Sentinel | Mizuki Sakurai
Prisoners of Aggregor
Bivalvan | Galapagus | P'andor | Andreas | Ra'ad
Charmcaster | Charmcaster's Stone Creatures | Charmcaster's Stone Animals | Argit | Baz-El | Simian
Generator Rex Heroes
Rex Salazar | Yumi Sakurakouji | Kenji Yamabuki | Bobo Haha | Agent Six | Rebecca Holiday | White Knight | Caesar Salazar | Akira Kazami | Ren Johnson | Edwin Bluestein
Future Heroes
Ben 10,000 (Ultimate Alien) | Ben 10,000 (Alternate Timeline) | Gwendolyn Tennyson (Alternate Timeline) | Shiori Sakurai (Alternate Timeline) | Gwendolyn Tennyson (Alternate Timeline) | Kenny Tennyson (Alternate Timeline) | Devlin Levin (Alternate Timeline) | Kaori Sakurai (Alternate Timeline) | Kaoru Sakurai (Alternate Timeline) | Max Tennyson (Alternate Timeline)
Main Villains
AggregorDiagonForever Knights (ConnorDriscollEnochJoseph Chadwick, Patrick, Red Knight, Sir Cyrus, Sir Dagonet, Sir Morton, Sir Reginald, Squire, Urian) • KhyberMalwareVilgaxZs'Skayr
Secondary Villains
AlbedoAloysius AnimoDNAliensElena ValidusEonFlame Keepers' Circle (Conduit Edwards, Esoterica) • HexKing ViktorLucubraMummyNegative 10PsyphonSixsixSevensevenSunnyVulkanusWill HarangueXenocyteYenaldooshiMichael Morningstar
Minor Villains
AdwaitaAggregor's SoldiersCamille's Ex-BoyfriendCarl NesmithCircus Freak Trio (Acid Breath, Frightwig, Thumbskull) • ClancyCoach FinnComputronEvil Way BigGarbage MonsterGorvanHighbreed Tree MonsterHiroshi SakuraiHowell WaynerightIncursion (Milleous, Attea, Sang-Froid, Frolic) • JarrettJennifer NocturneKrabbKolarMa VreedleMayor ColemanMizaruMorggMr. MannMrs. MannMyceliumNanochipsPalorfaygPickaxe AliensPlant AlienPlant ClonesR.E.D.Road Crew (Baron Highway, Road Rage, Turbine) • RojoRojo's GangSubliminoRagnarokS.A.M.Slix VigmaSquiresSsserpentSunderSynthroidTechadon RobotsThe Decoy QueenThe Great OneTrumbipulorVilgax's DronesZombozo
ArgitBaz-ElCharmcaster's Stone AnimalsHopeNull GuardiansSimianStone Creatures
Former Villains
BivalvanCashChromastoneDragonDeckaDevlin LevinEon's ServantsGoopHelen WheelsHighbreed (Reinrassic III, Highbreed Commander, Highbreed Councellors) • J.T.KenkoKevin LevinManny ArmstrongP'andorPrisoner 775Ra'adRetaliatorRyuji MaruyamaSACT (Lieutenant Steel) • Sentient Ultimate Big ChillSentient Ultimate CannonboltSentient Ultimate Echo EchoSentient Ultimate HumungousaurSentient Ultimate SpidermonkeySentient Ultimate SwampfireSir GeorgeSpidermonkeyTechnorgTetrax Shard • The Great One's Worshipers (Leader Alien, Enforcer Alien, Interpreter Alien) • Thomas JinglesVance VetteroyVictor ValidusVreedle Brothers (Octagon Vreedle, Rhomboid Vreedle) • Winston
Generator Rex Villains
AlphaBiowulfBlack KnightSkalamanderI-Bol
Future Villains
Exo-SkullKevin 11,000Vilgax (Goodbye and Good Riddance Timeline)
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