Kōga Gennosuke (japanese: 甲賀 弦之介, hiragana: こうが げんのすけ, rōmaji: Kouga Gennosuke) the primary male character in the Japanese anime Basilisk Kouga Ninpou Chou (known in English as the Kouga Ninja Scrolls). As the grandson of Lord Kouga Danjo, Gennosuke was chosen to be one of ten warriors to represent their clan of Koga Manjidani against the chosen ten of the rival Iga Tsubagakure clan. Upon his grandfather's death, Gennosuke ascends to take leadership of the clan.

In many ways, Gennosuke is as much an oddity among his clan as Oboro is among hers. An idealist and scholar who believes in looking to the future instead of being dominated by the past, Gennosuke views the pursuit of any grudge to be an ultimately pointless and self-destructive practice. His sense of principles remain even after learning of the renewed conflict between Koga and Iga, prompting him to lead the Koga on an expedition to Sunpu to plead with former Shogun Ieyasu and Hattori Hanzo the 4th to reinstigate the treaty before any more senseless bloodshed is caused.

Yet despite being a man of peace, if pushed into a corner Gennosuke is more than capable of killing anyone who threatens him or his clansmen. In addition to his skill with the sword, Gennosuke wields a power called Dojutsu which he learned from his teacher and uncle Muroga Hyouma. A hypnosis technique, Dojutsu reverses the homicidal intent of anyone who meets the stare of its user directly. In other words; if someone expresses hostility toward him, Gennosuke is able to will his enemies into killing themselves instead of him. Even Yakushiji Tenzen thinks twice before challenging Gennosuke directly.

Before the cancellation of the treaty, Gennosuke sought to build a lasting peace between Koga and Iga by marrying Oboro, the Iga Princess whom he loved to a great extent. His feelings for her remain even as the body count among both clans rises, filling him with torment as he struggles to reconcile his personal feelings with the duty demanded of him as his clan's leader. In the anime, Gennosuke carries with him a flute that he often plays for Oboro which represents their hope of unifying the clans in peace. After learning of the Hattori Truce's absolvement, he leaves the flute behind in Tsubagakure as a farewell present for her.

Gennosuke VS Iga Shinobi (episode 9): After successfully infiltrating Tsubagakure, Kasumi Gyoubu and Kisaragi Saemon informed Gennosuke of all that had occurred behind his back: the lifting of the Hattori Truce, the sneak attack on Manjidani, and the killing of several of the Koga ten's members. As he grimly realized he had to leave Tsubagakure and Oboro behind, the three Koga found themselves surrounded by a squad of Iga Shinobi led by Tenzen, Nenki and the other Iga ten. Gennosuke remained silent while a tirade of accusations and curses were hurled between his men and the Iga; not wanting to escalate the bloodshed anymore than what had already occurred. But when the ninjas under Nenki's command were ordered to attack despite Tenzen's warnings, Gennosuke was left with no choice but to use the Dojutsu; his power washing over the Iga shinobi and compelling them into turning their blades on themselves to the horror of all present; especially Oboro (who had been ignorant of what her clansmen had been doing the whole time). When Tenzen called the attack off, Gennosuke did the same and the Iga parted as he silently led his comrades out of the village without a word to even Oboro, who wept in sorrow as her hopes for peace and happiness appeared to crash down around her.

Gennosuke VS Koshirou (episode 9): Gennosuke had hardly made it to the village gate when he heard Chikuma Koshirou ordering him to turn and fight. Gennosuke warned his opponent to withdraw his challenge, but Koshirou refused to back down and hurled his scythes; only to miss as Gyoubu and Saemon knocked them aside. Koshirou then attempted to use his tornado power but had his technique neutralized when Oboro came between them in an attempt to stop the fight. Though Gennosuke was willing to walk away from their duel for the sake of sparing Oboro any further suffering, Koshirou attempted to create another vortex and Gennosuke retaliated with his Dojutsu to make his opponent's whirlwind backfire on himself; destroying Koushiro's eyes and rendering him blind. With his enemy immobilized, Gennosuke left Tsubagakure with Oboro's voice echoing in his ears as she pleaded for him not to leave her.

Gennosuke VS Kagerou (episode 11): Upon his return to Manjidani, Gennosuke decided to set out for Sunpu with the remaining Koga ten to discuss the meaning of the truce's cancellation with retired Shogun Ieyasu and Hattori Hanzo the 4th; asking his comrades not to let old grudges blind them to the fact that the Iga were people just like them and that the only way to truly end the violence was through understanding.

Stopping at a roadside inn, Gennosuke began to wonder if what the others had said about Oboro was correct and that she had willingly deceived him about the renewed conflict when Kagerou entered his quarters. After a brief conversation, Kagero hurled herself into Gennosuke's arms in an attempt to seduce him and began to poison him with her breath. Faced with imminent death, Gennosuke was forced to use his Dojutsu on Kagerou who began to suffer the effects of her own technique. As Gennosuke scolded her for acting so impulsively, Hotarubi's snake slithered through the window and struck for Kagerou. Gennosuke pushed her aside and decapitated the serpent with a flash of his knife. But with his body still suffering the effects of Kagerou's poison, Gennosuke was unable to dodge when the snake's severed head released a capsule that spilled the same Seven Days of Darkness potion Oboro had used on herself onto Gennosuke's face, sealing his eyes and effectively neutralizing his Dojutsu.

As Saemon and Kagerou set off in pursuit of Hotarubi, Gennosuke and Hyouma were attacked by Mino Nenki who was quickly dispatched by Hyouma's own Dojutsu. As Nenki's death throes echoed in his ear, Gennosuke thought of the remaining Iga who were almost certain to come after them next. But when he thought of Oboro, Gennosuke was unable to picture her as his enemy like he could only moments earlier; only as the sweet and gentle young girl he had fallen in love with.

Gennosuke VS The Wolf (episode 18): This conflict occurs only during the flashback of episode 18 of the anime. As a boy, Gennosuke was entrusted to the instruction of his uncle Hyouma by Lord Danjo in the hopes his grandson would learn Hyouma's Dojutsu technique. Much to Gennosuke's chagrin, Hyouma's teaching seemed to encompass nothing more than walking blindfolded through the forests surrounding Manjidani. After cutting his foot on a mountain pass, Gennosuke grew frustrated with Hyouma's seemingly incomprehensible methods and went for a walk; only to find himself confronted by a wolf with an injured paw. As the beast moved in a for the kill, Gennosuke suddenly activated his Dojutsu and the wolf retreated in terror. At that point, Gennosuke realized that Hyouma's instruction was designed to enhance his senses to allow him to tap into the Dojutsu and from then on, a mutual sense of respect and trust was born between them.

Gennosuke & Oboro VS Tenzen (episode 22-23): The climactic battle of the series. After being left behind by Kagerou and Saemon, Gennosuke went looking for them and learned that Kagerou had been captured by the Iga who threatened to execute her unless he answered Oboro's challenge to fight. Tracking the Iga to the Inn where they were staying under the protection of Lady Ofuku, Gennosuke was led to a nearby temple by his comrade's screams of pain and arrived just as Tenzen switched his attentions away from his torture of Kagerou to a second attempt at raping Oboro.

After cutting Kagerou from the pillar Tenzen had lashed her to; Gennosuke demanded to know why Tenzen was still alive when he was supposed to have been killed by Hyouma. Tenzen replied he lived in order to kill Gennosuke as he drew his katana and viciously threw himself into battle. Although blind and still unable to use his dojutsu, Gennosuke successfully held his own against Tenzen but still incurred several wounds that bled profusely while whatever injuries he managed to inflict on his opponent were instantly healed by Tenzen's demon. Slowly weakening from blood loss; Gennosuke inquired what was it that motivated Tenzen to be filled with such overwhelming wrath and Tenzen stated that as time went on, the Iga's reason for hating the Koga became hazy and unclear which threatened to end their longstanding grudge before it could be properly satisfied. Realizing that Tenzen had manipulated and used both clans to further his own agenda, Gennosuke held his position as Tenzen charged forward and permitted his opponent to stab him through the shoulder. With Tenzen now unable to block or avoid, Gennosuke grabbed onto his opponent's blade with his free hand and held Tenzen in place long enough to decapitate him with his sword.

With his enemy dead, Gennosuke called out for Oboro and demanded that she fight him so that an end could finally be brought to the war. In an effort to provoke her into attacking, Gennosuke told her his eyes had been sealed by the Iga and was shocked to hear Oboro admit that her eyes had also been sealed by her own hand. As Oboro pleaded for him to slay her before her eyes reopened, Gennosuke realized that Oboro had neither betrayed him nor intended to bring harm onto the Koga and was unable to raise his sword against her. With the other Koga and Iga dead, Gennosuke began to consider that perhaps he and Oboro wouldn't need to fight each other when Kagerou; dying and half-crazed from Tenzen's torture; demanded to know if Gennosuke was going to betray her, their clan, and their fallen comrades by letting his personal feelings corrupt his sense of duty. Knowing that the Takechiyo sect was bound to investigate the recent disturbance, Gennosuke lifted Kagerou into his arms to carry her to safety when Kagerou attempted to use her poisoned breath to take Gennosuke with her into the afterlife. Gennosuke's life was saved however by Oboro as her eyes finally became unsealed and dispelled Kagerou's technique before she could administer the killing dose. Alive but unconscious, Gennosuke was dragged by Oboro to underneath the front stairs of the temple where he regained consciousness long enough to tell Oboro he never wanted to kill her and quietly cursed himself for failing to prevent the bloodshed and pain caused by the fighting.

As Ofuku's samurai discovered Tenzen's remains and placed his head back onto his body, Oboro emerged from beneath the stairs and stared into his eyes to neutralize Tenzen's regenerative technique before he could fully revive himself as retribution for the crimes he had committed against herself, Gennosuke, and their clans. Unfortunately, Tenzen's symbiote had seen where Oboro had hidden Gennosuke and revealed his presence to Ofuku before Oboro had the chance to purge it from Tenzen's body.

Gennosuke VS Oboro (episode 24): The final battle of the series. Wounded, blind, and still suffering the effects of Kagerou's poison; Gennosuke was dragged half-dead by Ofuku's samurai to Sunpu where he was told that he would be facing Oboro at sunset in the final duel of the war and that both Hattori Hanzo and Ofuku would be witnessing their battle. What no one realized however was that Gennosuke had already decided that if he couldn't avoid fighting Oboro then he would permit her to slay him to both demonstrate his feelings for her and as an offering to the Iga for those he and his comrades had killed over the course of the ninja war.

As they stood facing each other along the same river their grandparents had fought and died on only 10 days earlier, Gennosuke kept his sword lowered and waited to be struck down when Oboro suddenly told him that she loved him. Confused, Gennosuke opened his eyes as the Seven Days of Darkness finally wore off and was horrified to see Oboro lying dead at his feet; the sword loaned to her by Kyohachiro plunged into her heart. Because Oboro killed herself, Ofuku lost hold of her sanity and ordered her samurai to kill Gennosuke before Oboro's death could be recorded on the battle scroll. But as the members of the Takechiyo sect closed in around him, Gennosuke had finally been pushed too far and he unleashed the full strength of his Dojutsu to compel Ofuku's samurai into killing themselves in one fell swoop. After taking back the battle scroll from Hattori Hanzo and the now emotionally broken Ofuku, Gennosuke cradled Oboro in his arms and bitterly wept before he used her blood to cross out both their names and record that Oboro was the last person to write in the scroll. After sending Ogen's hawk to deliver the scroll to Ieyasu, Gennosuke's final act was to carry Oboro into the river where he fatally stabbed himself in the hopes of being reunited with her in the afterlife.

But despite sacrificing their earthly happiness, Gennosuke and Oboro's sacrifice succeeded in moving Hattori Hanzo into negotiating a new treaty between their clans; thus breaking the cycle of violence, hatred, and death that Koga and Iga had been trapped in for 400 years and allowing the definite peace they and their grandparents had longed for to finally take hold.