Biba Amatori (天鳥 美馬, Amatori Biba), also known as the Liberator (解放者, Kaihousha), is the main antagonist of Kabaneri of the Iron Fortress. He was the eldest son of the Shogun, Okimasa Amatori whom had grow paranoid of the Kabane outbreak.
At 12 years old, he became the commander of 400,000 troops in the Battle of Kyushu where he was betrayed by the Shogun by essentially starving his army of their supplies. Biba swore vengeance against his father and spent the next decade forming the Hunters, a group of elite warriors and sought to claim the throne of Kongokaku.
He has long pink hair, and is called "beautiful" by the women in Shitori Station. He has the looks of someone who is used to fighting.
Not much is known about Biba. His ruthlessness and complex personality can be easily misinterpreted. It is yet unknown whether this twist in personality emerged after being betrayed by his father, or because of an inherent streak of callousness.
Biba taught Mumei that the weak die and the strong survive, and that one must choose to fight in order to be strong. He makes Kabaneris out of the "weak" and uses them as personal combat troops, perhaps by manipulating their need to be strong. Mumei's panicked words, "But I'm not weak!" when she was afraid of turning into a Kabane in episode 6 hints that Biba turns the Kabaneris he deems weak into Kabanes. He has a policy of "discarding" or banishing people who are too injured to serve, as Enoku and Mumei notes. In Enoku's case, Biba harbored suspicions about Enoku's loyalty.
Mumei, also known as Claw of the Liberator, addresses him as "Brother" (兄様, Ani-sama). She looks up to him to the point of idolatry, frequently quoting him and even talking to him in her sleep. She even goes so far as to hit Ikoma and call him a liar when defending Biba against Ikoma's accusations. However, Biba does not appear to genuinely reciprocate her affection, only praising her to use her.
Biba appears to be very charismatic, judging by his popularity with the common people and the respect he commands from Mumei, despite the fact that he renamed her "Mumei", which means "Nameless". Even Enoku, known as former Ear of the Liberator, desperately wanted to "continue serving the Young Master away from the front lines" by acting as a double agent. It is implied that Enoku faltered in his mission years ago and is thus dismissed. Biba reads Ikoma easily and knows exactly what to say to win instant kinship.
Biba is politically astute and deceptive. The antithesis of Ikoma, he garners a reputation as a Kabane exterminator and land liberator for the people, but his true goal is to reach Kongoukaku and organize a coup to seize power from his father and obtain revenge for being betrayed. He tries to manipulate Mumei into robbing the master key from Ayame, after gallantly offering to "escort" Koutetsujou to Kongoukaku. A cunning strategist, Biba sees through his enemies' numerous attempts at assassination very quickly.
Biba is obviously very skilled in combat with a gun-sword coated with Kabane heart metal, and commands his battle horse at an almost psychic level. He devises the Hunters' effective battle strategies himself, and is gifted at military leadership. It is suggested that Biba trains his Hunters himself.
Making Biba even more dangerous is his skill with technology or resources he has at his disposal. Biba's Hayajiro, the Kokujou, is extensively modified and carries perhaps the most advanced Kabane technology or research. It is revealed that he was the one who turned Mumei into a Kabaneri. The Kokujou has an experimental center/makeshift interrogation chamber that keeps an artificial Kabane fused colony called the Tsutsugamidokoro. Biba works on the Kokujyo himself, suggesting he is at least as good as Ikoma at engineering. Whether he wanted to work on the engine himself in order to impress his visitors, or because he trusts his own workmanship more is unknown.
Ikoma strongly believes that Biba is no hero at all, since he witnessed Biba smiling when he disarmed and killed Enoku in cold blood after Enoku's failed attempt at assassinating Biba.
Biba was born in Kongokaku as the son of the Shogun Okimasa and an unnamed mother. As a child, Biba greatly loved his father, with one memory depicting the two happily riding on a horseback, the only gift which Biba ever received from his father was a Tantō which he treasured dearly.
Over time however, his father grew paranoid of the Kabane outbreak, one night, he extinguished all the lights in their home and repeatedly slashed Biba’s back in a state of panic. Biba visibly shocked by his father, whom attempted to defend his cowardly actions had been caused by fear, following this, Biba gradually alienated himself from his father.
At the age of 12, Biba became the commander of the army of over 400,000 troops whom had been dispatched by his father to Kyushu in order to exterminate the Kabane threat. Upon arrival, Biba and his forces initially maintained a strong position where they established several bases and succeeded in holding back the Kabane. Later however their replacement supplies were eventually cut off and as a result, Biba’s forces were soon defeated leaving Biba emotionally devastated.
Upon learning the discovery that his father was purposely behind his defeat, Biba developed an intense hatred towards him for his betrayal. Biba later spent the next ten years forming a group of elite warriors named the Hunters.
Mentioned through the series, he was first seen in a flashback of Mumei in episode 6, where he saves Mumei from being killed by a frightened bushi after her mom is shot.
In episode 7, he leads the Hunters, a group of people who eradicate lands filled with Kabane and reclaim them for people, into Shitori Station. Even though he is the eldest son of the Shogun, it appears that he is an independent force, as he has enemies in the Shogunate intent on bringing him down. Enoku tells Mumei to warn Biba in episode 5, and proclaims his allegiance to Biba.
Biba harbors a deep insecurity of being betrayed and back-stabbed. To compensate for his father's betrayal on the battlefield years ago, he adopts an extreme worldview, which he passes on to Mumei: "Live on your own. Don't rely on others." He also ruthlessly kills and murders those whose loyalty he doubts eg) Enoku. Even more frighteningly, he seems to subject servants he suspects to the interrogation chamber/Kabane experimental center Tsutsugamidokoro. When Ikoma confronted Biba over his worldview, Biba sends Mumei off to the Tsutsugamidokoro for revealing such personal and controversial information. It is unknown what occurred, but Mumei is next seen waking up on the medical examination table. Next, Biba sends her on a mission that will test her true allegiance - to steal the master key from Ayame. He is quietly pleased when she discovers that Yukina and Ayame had lied to her.
Biba does not appear to have any close relationships or fighting partners. He keeps his relationships professional, although he shows regret or sadness when his servants die. This avoidance behavior could also be due to the betrayal he experienced, or the hard life of the battlefield. He is mostly seen around Mumei.
Mumei is one of his closest soldiers, and was the only Kabaneri left on the Kokujou when she was dispatched on a secret mission. She is not irreplaceable though; Biba had already created another when she returned, called Horobi. Mumei is the only hunter that calls Biba (or is allowed to call Biba) "brother". She is also the only one who treats him like family, understanding his true goal of reaching his home, Kongoukaku. However, Biba readily refutes assumptions that she is his sister, perhaps to thwart political enemies who would use Mumei against him.