Weed encounters Jerome and his squad of assassin dogs who hunt the mutant Kaibutsu. Jerome explains that Kaibutsu,also known as P4, escaped from a research laboratory years ago after killing humans. The squad intends to use Weed as a decoy to lure the monster out of its fortress, Gajou. Jerome and his comrades leap across a dangerous cliff to reach Gajou, and Weed follows with Smith and the others. The group agrees to Jerome's plan, and North guides Weed deeper into the fortress. Kaibutsu attacks suddenly, killing North and throwing his corpse out of Gajou. Weed attempts to tear Kaibutsu's exposed chest arteries but only manages to tear its skin. Smith, refusing to let Weed die in vain, enters Gajou alone and bites onto Kaibutsu's neck. Kaibutsu smashes itself and Smith against the rocks repeatedly, causing hundreds of rocks to crash down on both of them. The other dogs drag Smith's crushed body out of Gajou, where Weed, GB, and Mel mourn his death. Smith's final words instruct Weed to tell his father Gin that Smith is sorry for losing sight of Sakura. Inside Gajou, Kaibutsu survives the collapse and questions why dogs take the side of humans, leaving the mission incomplete.

A helicopter carrying one of the human scientists previously attacked by Kaibutsu approaches Gajou. Kaibutsu leaps out and roars,causing three dogs to flee. He questions why the dogs support humans, directing his words specifically at Jerome. Jerome responds that humans are dogs' natural partners and that Kaibutsu, once a dog himself, has committed the unacceptable act of killing and eating humans. Kaibutsu reveals that humans betrayed him through torturous genetic experiments that mutated his appearance. He reminds Jerome how Jerome once comforted him during those experiments, giving him strength to endure the pain. Kaibutsu declares he has lost all positive emotions and become a true man-eating beast. GB, Ken, Kagetora, Weed, and Mel attack him in anger, but Kaibutsu pushes them away. Jerome's group runs to the other side of Gajou to lure the monster, with Jerome calling him by his laboratory name P4 to provoke him. Robert, Rocca, and Heuler attack on Jerome's command and inflict a deep chest wound, but Kaibutsu kills all three. Weed and the others hold Kaibutsu still while Jerome bites deep into his chest arteries. Kaibutsu grabs Kagetora, but Jerome nips the arteries again, forcing Kaibutsu to release him. Kaibutsu pulls Jerome off, but Jerome catches his jaw and drags him down into the gorge. Kaibutsu survives, biting Jerome's ribs and climbing back to the cliff edge with Jerome in his mouth. Kagetora states that his uncle Akatora died sacrificing himself to wound an enemy so others could finish it, just as Jerome's squad did. Kaibutsu throws Jerome down the gorge. Ken, Kagetora, and Weed, consumed by rage, push Kaibutsu off the cliff. All four begin falling toward the gorge floor, and Weed realizes that their current trajectory will kill all of them.

Weed's army advances across the open field toward Hougen's stone fortress. Hougen observes from the highest tower and orders Genba to lead two hundred soldiers in a counterattack. Genba's force charges downhill,colliding with Weed's front line near the dry riverbed. Weed commands his troops to form a wedge formation. The wedge splits Genba's forces into two smaller groups. Jerome's flanking unit attacks the separated right group from the rear. Kyoushiro leads a second flanking unit against the left group. Genba attempts to rally his soldiers, but Weed personally engages Genba. Weed dodges Genba's lunge and bites Genba's front leg, breaking the bone. Genba falls and cannot stand. Hougen sees Genba's defeat and descends from the tower with ten elite guards. The guards form a ring around Weed. Hougen throws a mouthful of dirt into Weed's eyes, temporarily blinding him. Hougen strikes Weed's side with his claws. Weed shakes off the dirt and retaliates by biting Hougen's left ear. Hougen screams and tears himself free, losing part of his ear. Hougen flees into a narrow tunnel entrance behind the fortress. Weed pursues into the tunnel. Inside the darkness, Hougen claws at the tunnel ceiling, causing a collapse. Rocks fall between Weed and Hougen, blocking the path. Weed digs at the rocks but cannot clear them quickly. Hougen escapes through a hidden exit on the mountain slope. The episode ends with Weed hearing Hougen's distant howl of revenge from the mountain.

The Ohu army returns to the Koga village to leave Kyoshiro's pups behind. The pups,led by Teru, refuse and insist on fighting. Weed calmly explains that the adults have no right to steal the pups' future, and the pups finally agree to stay with the Koga elder. Tesshin and his ninja dogs join the Ohu army. At Ohu, Akame spots Genba's minions capturing female dogs for Hougen. Akame takes Kurotora and Hook to stop the hunting and sends Mel to warn Weed. Mel encounters Hougen's army carrying an injured Gin and spies on them. Weed's army heads to Hougen's hut in the Alps, unaware Hougen has already left with Gin. The assassins Lecter and Thunder ambush Weed and Tesshin inside the hut. Weed uses an old knife to chop off Lecter's fangs and forces information from them. Lecter reveals Hougen took Gin to Ohu. Weed spares the assassins on condition they leave Hougen, but Jerome stays behind suspicious. Jerome follows Lecter and Thunder, overhears their plot to kill Weed, and kills Lecter. Weed arrives to see Jerome pinning down Thunder and orders him to stop, but Jerome kills Thunder as well. Weed banishes Jerome from the pack for becoming a killer again. Kyoshiro's pack leaves with Jerome, calling Weed weak, but Jerome admits Weed was right and departs alone to recruit more dogs from Shikoku.

Hougen prevents Kamakiri from executing Genba's defeated soldiers and instead orders a tournament to select top generals. Four dogs—Kite,Batt, Buruge, and Toube—emerge as Hougen's elite fighters. The Ohu army continues toward Futago Pass as Kyoshiro's group follows. Kyoshiro chases Mel, who mistakes him for an enemy, but Mel reaches Weed and reports Hougen's invasion. Weed thanks Kyoshiro for returning, prompting Kyoshiro to join the Ohu forces. At Gajou, Genba departs with Toube to steal females but encounters Shigure and the six sons of Kisaragi from Mutsu. Genba orders Toube to attack the newcomers. Weed, Tesshin, and others arrive as Genba pins Akame. Tesshin stops Weed from engaging Genba, declaring himself sufficient for the fight. Tesshin uses ninja-dog techniques to inflict deep cuts on the Great Dane multiple times. Akame senses an approaching strong blizzard and drags Izou to safety. Kamakiri's reinforcement army arrives at Hougen's command to rescue Genba. Tesshin and Shigure give Genba a chance to surrender, but he refuses, so they grab his shoulders and push themselves and Genba off a cliff. The predicted blizzard hits, blinding both armies and forcing them to withdraw. The next morning, Tesshin and Shigure return, reporting that Genba hit his head on a rock and will likely never return to battle. At the cliff base, Genba wakes, attacks his own soldier, and collapses again, leaving him brain-damaged and suffering memory loss. Toube reacts with horror while Kamakiri smiles at Genba's downfall, seeing a chance to become Hougen's second-in-command.

At Gajou,Hougen mourns his brother Genba's injuries. Genba wakes and attacks the surrounding dogs, displaying severe brain damage that prevents him from recognizing Hougen. Genba bites Hougen, who realizes his own brother cannot identify him. Hougen tearfully bites Genba's head and swiftly kills him as an act of mercy while Toube and other dogs watch. Hougen licks his dead brother's cheeks and remembers their birth in an abandoned shack where a breeder left them without food, forcing them into cannibalism to survive. The one-year-old Hougen and Genba killed and ate the breeder upon his return, then made a promise that the surviving brother would kill the other with his own fangs. Two dogs from Genba's army attempt to leave, claiming they need to treat injuries, but Hougen furiously kills them both. Hougen orders the remaining escaping dogs pinned down and kills all of them. Toube fights Hougen, but Hougen defeats him and destroys one of his eyes. Hougen throws the corpses and the still-alive Toube into the river below the gorge. At a hidden location, Akame introduces Weed's army to Ben and Cross. The Ohu army spots Kamakiri's army searching for them by scent. Weed devises a plan to lure and trick the enemy, taking Rocket with him. They deliberately reveal themselves to Kamakiri's army, who chase them. Weed and Rocket lead the army into a small ravine where many enemy soldiers fall. Weed hides beneath a narrow river, going unnoticed by Kamakiri's army. Rocket leads the pursuers through the same paths repeatedly for a long time without their realization. Weed's army suddenly appears spread across the cliff edge, creating the false impression of larger numbers. Weed offers Kamakiri's army a chance to leave, but Kamakiri refuses, calling withdrawal dishonorable. Another group of dogs appears at the cliff edge, terrifying Kamakiri into believing a massive force hides behind the visible soldiers. GB, Ken, and Kagetora run in circles, shouting that they came from Hokuriku to help the Ohu army, further inflating the perceived reinforcements. Kamakiri becomes too frightened to fight and withdraws with his army. Weed meets the new arrivals led by Moss the English Mastiff and Musashi the Tosa dog, both old Ohu comrades. Moss informs Weed that Jerome notified them of the situation and summoned them. Moss adds that Jerome separated from them on the way. Weed senses Jerome nearby, but when the group decides to search for him, Jerome leaves with four Shikoku dogs placed to protect him. Weed cannot forget or forgive Jerome, and both dogs begin crying as they move further apart. The episode ends with Jerome's departure and Weed's unresolved emotional conflict hanging over the Ohu army's next move.

The Ohu army encounters a dog named Shingo who claims his friend is drowning. Kyoshiro identifies Shingo as one of Hougen's soldiers,but Weed leads the group to follow him anyway. The dog in danger is Toube, and the army pulls him from the river while Musashi watches from a distance. At Gajou, Hougen learns that the Ohu army has gathered over three hundred soldiers and nearly chokes Kamakiri to death, warning him of execution if his next mission fails. At the Ohu army's hideout, Moss, Musashi, and the other veterans weep upon receiving the fang of the deceased John, delivered by Hook. Musashi reveals to Toube that during his fighting dog days, Toube was the only dog who ever defeated him. Toube explains he joined Hougen's army to fight on a battlefield where Musashi was present, but now seeks revenge on Hougen for his mistreatment. He collapses from exhaustion as he tries to leave the hideout. Escaped soldiers Shingo and Kerry thank the Ohu army, but when Kerry proposes returning to Hougen to falsely report the army's size, Jerome ambushes and threatens him, causing both to flee. GB leaves to find snake meat for Toube, accidentally enters enemy territory, and infiltrates Gajou under the false name JinBei, where he discovers Gin held unconscious and weak. Outside Gajou, GB reunites with his old friend Sasuke, who reveals Hougen's minions captured him and forced him into labor. When two of Hougen's soldiers discover their escape plan, Weed, Ken, and Kagetora arrive to rescue GB and Sasuke. GB regains consciousness and reports Gin's location to Weed, while Sasuke accidentally reveals that GB is Weed's godfather. Toube decides to join the Ohu army, recognizing that both he and Weed share the same goal of defeating Hougen.