Samurai Warriors Edit

Kotarō is the wild card in the series who strives to perpetuate endless chaos. When his master hears ofIeyasu's retreat at Mikatagahara, he is ordered to assist Shingen with the pursuit. Although he does capture Ieyasu, Kotarō also kills Shingen to counteract the results. In a bid to spare their lives, Ieyasu and his men are forced to serve Kotarō and surrender to the Hōjō.

During his time of leisure, Kotarō learns of Nobunaga's infamous "Demon King" reputation. Thinking at first that Nobunaga desecrates the demon name, he rides alone to disrupt the battle at Ōsaka Bay. Kotarō eventually sees the man himself and foresees his adversary's fiery end. More amused by the image, he decides to stay his hand and leaves Nobunaga to his fate at Honnōji.

Power shifts to Hideyoshi and the large Tokugawa-Hōjō army lay siege to his residence, Ōsaka Castle. Hanzō, who is displeased with Ieyasu's enslavement to Kotarō, seeks to liberate his true master. Intrigued, Kotarō challenges his rival to a contest to see who can kill the land's unifier first. If Hanzō wins, Ieyasu would be freed.

After Hanzō's failures and Hideyoshi's death, the Hōjō become leaders of the land. Bored with the idea of peace, Kotarō betrays and kills his benefactors at Odawara Castle to pollute Japan with confusion. Left with nothing else to do, Kotarō decides to aim for unification himself and heads with his army to Kyūshū. Seeing a large force of Hideyoshi's former retainers there, Kotarō relishes the land's last grand battle. In his ending, he rewards Ieyasu's loyalty by giving him ownership of the land and cryptically disappears.

His dream stage has him protecting the Hōjō clan at Odawara Castle. Faced with the massive Toyotomi army, he also needs to fend off the Tokugawa forces. While doing so, he has to stop Nene's interruptions.

Samurai Warriors: Katana includes Kotarō in the Ascendancy scenario as the player's final opponent. When Nobunaga comes close to claiming victory at Sekigahara, the shinobi incapacitates him from behind in an effort to prolong the chaos; his assassination attempt is thwarted by the protagonist. The Stealth scenario has Kotarō fulfill his obligations to the Hōjō by retaking Kawagoe Castle from the Uesugi army. However, their failure to acknowledge the Fūma clan's contribution insults him greatly. His disdain for them intensifies when Ujiteru's ineptness at Mimase Pass costs him the lives of his own comrades. As Kotarō's faith in the Hōjō irreversibly deteriorates, his relationship with the player grows to the point where they conspire to overthrow their masters at Odawara Castle.

Having succeeded in his rebellion, he goes on to invade Mikawa while Ieyasu is away. By the time the Tokugawa forces return, they are too late to undo the damage done during their absence. The rogue ninja relishes in their annihilation and creates an age of chaos to satisfy his twisted philosophy. While making plans to attack west, he is unexpectedly betrayed by the player who rejects his despotic rule. Amused by this turn of events, he tests the defector's resolve at Ōsaka Castle by pitting him against his former allies. Their eventual duel ends with Kotarō's defeat. He willingly accepts this outcome and embraces death so that the protagonist may begin a new era for the people.

In Trial Mode, Kotarō is one of two people suspected of harboring stolen treasure within the Bamboo Room. His defeat clears him of the theft, forcing the player to repeat the mission in order to pursue the other culprit.

While Kotarō lacks a personal story mode in Samurai Warriors 3, he continues to serve the Hōjō and appears in Ujiyasu's campaigns as a secondary general. He seems to be more loyal to the Hōjō in this installment than the last. He lives as late as the Ōsaka Campaign to ambush and strike chaos into any who cross his path. Kotarō will randomly join any side that he thinks is appropriate, which ranges from Mitsuhide's army at Iga, theMōri in random scenarios, and the undermanned Toyotomi at Ōsaka.

For his story in the Xtreme Legends expansion, Kotarō continues his service to the Hōjō. Before he is called to his duty to protect his master at Tonegawa, he has a chance encounter with the wild man, Keiji. As Ujiyasu orders his men to repel the Uesugi offensive, Kunoichi leads Shingen's reinforcements for their assistance. When she is surrounded by Uesugi generals, Kotarō is ordered to rescue the young kunoichi in order to save face for Ujiyasu. Kotarō also crosses blades with Keiji in the battlefield, each participant enjoying their first match against one another. The shinobi's efforts causes Kenshin's retreat back to Echigo and spurns Shingen's march to take Odawara Castle. When his ploy fails, Shingen pulls back with Ujiyasu's sons leading the pursuit. A worried Ujiyasu decides to aid his sons' armies when they fall victim to one of Shingen's plots. Due to the pact between them, Kotarō follows Ujiyasu to Mimasetōge.

After their victory, the player is entreated to a dream of Ujiyasu's first meeting with Kotarō and the meaning of their pact. Ujiyasu is only a child at the time and is ashamed to be called a coward. Lamenting for being scared by the sound of a firing rifle, the young boy is ready to take his life. An eavesdropping Kotarō reasons fear essential for being human, stating the courage the boy desires only makes them hollow. Kotarō's sudden appearance frightens the boy, but he trusts his words. He asks the "ghost" to take his suicidal dagger away from him, least he believe in foolish courage again. Congratulating the boy for his decision, Kotarō offers a pact between them. When Ujiyasu awakens, Kotarō is beside him and patting his head like he did several years before. Though disgruntled upon seeing him, Ujiyasu thanks the shinobi for helping him protect their pact. Kotarō leaves behind the dagger from the daimyo's childhood before disappearing from the Hōjō houshold. Ujiyasu dies of illness soon after.

Choosing to wander with his master gone, Kotarō happens to spot Keiji at Shizugatake. To aid his rival, he joinsKatsuie and Toshiie's side of the conflict. Their efforts drive back Hideyoshi, but Toshiie has a change of heart when he fears they might gain total victory. Redirecting their attention towards Katsuie, Kotarō decides to race Keiji to see who can defeat him first. When the eastern regions fall into internal rebellions, Ieyasu and his Hōjō allies work together to take Ueda Castle. Kotarō feels nostalgic for his ties to the Hōjō and returns to serve in their ranks. A happy Kai rejoices his arrival, stating she wants to grow up and make their late lord proud. When she asks the shinobi to watch over her progress, Kotarō remarks he once had someone ask the same of him long ago.

With Hideyoshi claiming his name throughout the land, it is only a matter of time before he sets his eyes on the stubborn Hōjō within Odawara Castle. Kotarō decides to protect Ujimasa and Kai, interested in letting them live past the conflict. Demolishing the oppressing army sent against them, Kotarō eventually corners Hideyoshi. Frustrated by the shinobi's disinterest in a peaceful world, Kotarō simply tells the daimyo to eradicate him. Keiji volunteers to try to best the shinobi in a final duel but loses. Seeing no use for chaotic ones such as themselves in a land of wealth and prosperity, Kotarō spares his opponent and accepts his apparent death to Hideyoshi's archers. As others gradually leave the area, the shinobi uses ventriloquism to convince a distressed Kai that his soul lives on within a puppy's body. Though "he" would soon lose his ability to talk, Kai promises to protect "Kotarō" with her life. Faraway, the real Kotarō is pleased by her reaction and vanishes.

He continues his service to Ujiyasu during the warlord's scenario in Sengoku Musou 3: Empires by providing information on the other clans' movements from time to time. He personally carries out his lord's plan to make the Imagawa their allies by inciting the Oda to threaten Yoshimoto's territories. While watching their allies play kemari in the story's ending, Kotarō asks Ujiyasu if he's content with being the land's caretaker only to receive a sarcastic retort.

Kotarō acts as Ujiyasu's cryptic advisor in Samurai Warriors 4. While Ujiyasu broods over his decisions, Kotarō often suggests becoming ruthless to obtain his goals. The shinobi is amused when his opinion is generally ignored, seeking to watch over the results of his lord's judgment. Catching onto the daughter's behavior, he keeps tabs on Saburō to prevent her from brashly running away to see him. Kotarō serves the Hōjō in their every campaign, even accompanying the maiden's attempt to reinforce Saburō in the Uesugi civil conflict.

Kotarō briefly interrupts the Toyotomi's forces at Kyushu. He reports his findings to Ujiyasu to prepare for their defenses at Oshi Castle/Odawara Castle. Following Ujiyasu's demise, Kotarō wanders as he pleases and decides to resist unification a final time at Ōsaka Castle. Whether he lives or dies in battle is left to the player's discretion.

The 4-II Pledges of Honor has him act as Lady Hayakawa's guardian who keeps discrete tabs on her. She asks him to keep an eye on Saburō for her when they separate. Kotarō watches over Kai and Lady Hayakawa's reunion at Ōsaka Castle before disappearing.

Kotarō is the leading man for the third downloadable scenario. Sometime during Hideyoshi's unification, a spell has been cast on the land. The samurai leave their stations and act completely out of character under its trance; the ninja are immune to it. Since Lady Hayakawa is among the victims, Kotarō summons the other ninja to assist his purge of the spell caster. Hisahide boasts himself as the puppet master, but Kashinkoji is the one pulling the strings. Kotarō robs the illusionist of the incantation for his safe-keeping. After the samurai are liberated, Kotarō uses the same spell on the other ninja for a laugh.