Ken Oyanagi

"Hey, mister. Wanna play rock-paper-scissors?"

- Ken Oyanagi

Ken Oyanagi (大柳 賢), originally referred to as, is a tertiary antagonist featured in the fourth part of JoJo's Bizarre Adventure, Diamond is Unbreakable, specifically in the "Janken Boy Is Coming!" story arc.

Ken is an ordinary child made into a Stand user by Yoshihiro Kira and prompted into challenging Rohan Kishibe in a game of rock-paper-scissors in which the latter must gamble his own Stand. Ken's ability is named Boy II Man.

Appearance
Ken is a young boy of short stature, slim build, and medium straight hair. His attire consists of a headband, open ankle-high sandals and with both straps on one shoulder; the garment is adorned on all sides by several large safety pins.

On his left cheek, is a large hole produced after being impaled with the Arrow.

Personality
Ken's wish is to become an adult who is respected just as much as Rohan. He has no real knowledge of Stands at the start, but he quickly learns more as the match progresses. He is decisive in his actions, willing to sacrifice himself after being defeated and taking a baby hostage to get another match against Rohan. He heavily believes that luck is on his side. Rohan describes him as a typical bouncy kid with an ordinary life and no family problems upon using Heaven's Door on him.

Otherwise, Ken is stated to behave like any ordinary bouncy child. According to Heaven's Door, Ken reads Shōnen Jump every week and is in sixth grade at his school. He loves soccer but played baseball until his coach complained about his long hair and he was forced to quit (while blowing his nose on the coach's hat). He also hates peppers and anpan, likes fatty cuts of meat, is afraid of the dentist and Namahage, and has never used a public restroom. He also has no family issues. During the climax of his fight with Rohan Kishibe, Ken exclaims "Good!", similar to Daniel J. D'Arby.

Stand
Boy II Man is a Stand that enables Ken to steal someone's Stand when the latter participates in a five-round game of rock paper scissors with him and loses. Each round lost causes the victim to lose a third of their power and Stand to Ken. An ultimate win from the victim's part returns the full Stand.

Background
Ken Oyanagi is a citizen of Morioh. He lived an ordinary life as a kid until he crossed path with Yoshihiro Kira, whose Arrow recognized as a potential Stand User as he was climbing a telephone pole to steal fruits. Yoshihiro struck him in the cheek, creating his hole and making him a Stand User. The boy develops the ambition to defeat Rohan at a game of rock-paper-scissors to earn the respect of others.

Diamond is Unbreakable
Ken Oyanagi proceeds to approach Rohan Kishibe and harasses him in order to play rock-paper-scissors with the mangaka. He confronts Rohan a first time at the train station, while Rohan is investigating the crowd of commuters. Rohan tries to ignore him but when Ken insists, he uses Heaven's Door to read his bio. Reassured that Ken isn't a Stand User (unaware that Ken just became one and isn't completely aware of his ability), Rohan tries to go away but Ken tries take a taxi in his stead. Angered by the kid's insistance, Rohan accepts to play to see who gets the taxi. Rohan wins with "rock". Later, Ken finds Rohan at the "Café deux magots" and takes his seat at the only free table; when Rohan protests, the boy makes a scene and loudly cries to embarrass Rohan. Thus, he forces Rohan again to play again to see who gets the table. However, Rohan wins with "paper".

Ken follows Rohan up to a bookshop where he takes a book Rohan was interested in and wants to buy. Truly angered, Rohan accepts to play again but punches the kid instead. However, Ken takes the round as a win because Rohan's closed fist counts as a "rock" and he played "paper". Thus, Ken summons his Stand Boy II Man which takes a third of Heaven's Door's power. While Rohan turns Ken into a book, the power the boy has stolen allows him to cancel the ability. Moreover, he takes control of Rohan's right arm. Rohan realizes what the rules of the game are and is forced to win a third round of rock-paper-scissors to get his Stand back. However, Ken wins the fourth round with his "paper". Boy II Man steals Heaven's Door's legs, sapping Rohan's leg strength.

Ken now feels confident as his luck is on the rise. When Ken and Rohan play the fifth round, Rohan aims to play "rock" while Ken aims to play "paper". Luckly, Rohan trips and the unusual movement instills doubt in Ken's mind, who changes his "paper" to "rock". Rohan seems reassured, but Ken then tests his luck by shouting as a passing Josuke Higashikata and Joseph Joestar, betting that they will not come. Indeed, Josuke doesn't want to interact with Rohan and tells his father to smile and wave back, then leave. Then Ken breaks a window and purposefully stands under the falling shards, coming out unscathed while Rohan's hand is wounded. Thus, it proves that Ken's luck is at its peak.

However, Rohan is still determined to play the last round. Rohan plays "paper" while Ken plays "scissors", but his fist suddenly close, making it into a "rock". Ken loses the round and the game, thus Rohan's powers are returned to him. Rohan explains that he took Shizuka Joestar, the invisible baby, and made her close Ken's fist to win. Angry, Ken takes Shizuka hostage and demands a new game, to which Rohan accepts. However this time, Rohan easily wins. Rohan approaches to seal Ken's ability forever but desperate, the boy throws himself in the path of a truck to kill himself. Amused, Rohan steps in front of the truck too, as Yoshihiro Kira's photo flies into the truck's windshield, forcing the driver to swerve hard. Rohan and Ken are thus unharmed. Ken's impressed by Rohan's luck, is convinced not to use his Stand ability to harm others. However, they now have to look for Shizuka, which has turned invisible.

Trivia

 * In the English dub, Ken's nickname is changed to "Rosham Boy" as a pun on "roshambo", another name for Rock-Paper-Scissors.