BUSO RENKIN

The story begins when high school student Kazuki Muto (武藤カズキ Mutō Kazuki^?) is killed one night saving a mysterious girl from a monster, only to wake up in his school dorm, believing it to have been a dream. However, he soon finds out that dream wasn't a dream at all when a giant serpentine monster attacks him and his sister. Tokiko Tsumura (津村斗貴子 Tsumura Tokiko^?), the girl he saved, explains that the monster is a homunculus. Kazuki had been attacked and killed by it when rescuing Tokiko. However she, feeling responsible for him, revived him by placing aKakugane medallion in his chest, serving as a replacement heart.

The Kakugane, as Tokiko explains, is an alchemical (alchemistic) device that, when activated, takes a certain form based on the Kakugane's user, forming a unique Buso Renkin. The Buso Renkin is the only thing that can destroy a homunculus monster. Using this, Kazuki creates his own Buso Renkin, taking the form of a giant lance, later named 'Sunlight Heart'. Along with Tokiko and her own Buso Renkin (the Valkyrie Skirt, an execution scythe), Kazuki joins the fight against the homunculi and their master.

Alchemy

In the world of Buso Renkin, there are two types of alchemy besides the historical one: buso renkin (arms alchemy) and homunculus. In this world, these are the only categories of alchemy which had succeeded, while the attempts to transform base metals into gold or achieve immortality had failed.

Buso Renkin

Buso Renkin are weapons formed by the alchemically-created kakugane, based on the user's will to fight. The shape the Buso Renkin takes reflects the user's personality. Buso Renkin are the only weapons known to be able to kill a homunculus. Kakugane are developed in the process of creating the Philosopher's stone, the ultimate goal of the Alchemy Warriors around the planet. Kakugane will generate a weapon that reflects the user's battle style; a user will always have the same type of Buso Renkin regardless of the Kakugane number, though there will be cosmetic differences. Buso Renkin are activated by the fighting instinct of the user. This means that they can only be used by humans or human-type homunculi, since only humans have the instinct to use tools to defend themselves. Kakugane, in their normal state, can also strengthen a user's healing abilities. In total, there are only 100 Kakugane, from I (1) to C (100). The first three of were turned into Black Kakuganes and the second one was made into a White Kakugane afterwards. After the Victor Incident, Kakugane were scattered around the world; currently, there are 25 known Kakugane that are used in Japan.

Black Kakugane

Black Kakugane I-III are the first results of the Alchemy Warriors. However, they were unstable, and upon insertion of Black Kakugane I (1) to replace his heart, Warrior Victor lost control. The same thing would happen to Kazuki 100 years later when his Black Kakugane III awoke. A person who has been revived using a black Kakugane is called a 'Victor,' since he was the first person to become such a being. Black Kakugane give their users glowing light green hair, red eyes, and tanned skin, with the ability to use 'Energy Drain,' a 'vital body function' which absorbs people's life force; it's possible to kill a person by draining his/her energy. As it is a vital body function, it is impossible to stop or shut off. Black Kakugane users also have the ability to evolve. While in stage 1, a user can transform from normal human to his/her 'Victor' form. After six weeks, a user evolves into stage 2, when he/she is permanently transformed into a 'Victor' form. After more time has passed, the person may willingly change back and forth from stage 3 where the tanned skin turns into a dark red, and the power of energy drain greatly increases. Black Kakugane have all the functions of a standard Kakugane. Buso Renkin created by Black Kakugane tend to be much stronger, since they make their users' bodies so much stronger.

White Kakugane

Developed by Alexandria, a White Kakugane is the exact opposite of a Black Kakugane. It holds the ability to nullify a Black Kakugane's power, restoring a person with a Black Kakugane to normal.

Kazuki's Kakugane that Tokiko took back from Alexandria was a 'test model' that was disguised as a normal kakugane. However, it proved to be unstable when it was in close proximity with a Black Kakugane; in this case, Victor's Black Kakugane I. Alexandria then developed another kakugane based on Black Kakugane II, moving past the test stage. This Kakugane was used in an unsuccessful attempt to restore Victor to normal; a Black Kakugane user in stage 3 can only be restored to stage 2.

Papillon was able to make a White Kakugane based on his own knowledge and the research Dr. Butterfly and Alexandria left behind. Using them, he was able to develop a White Kakugane from scratch, and used it to change Kazuki back to normal in Buso Renkin Period. His devices were then used to create another White Kakugane to restore Victor back to normal. Other than the converted Kakugane II, the other two White Kakugane's are not numbered as they were not the original 100 Kakuganes. It is possible to have more than one White Kakugane in a person's body, as shown by Victor, who has two White Kakugane in his body by the end of the story.

Homunculus

A homunculus is created when an embryo-like creation from a plant, animal, or even a human is placed inside a human. The embryo then invades the brain and takes control of the body, giving it abilities that mimic the natural talents of the embryo's origin. They can all regenerate from virtually any wound inflicted on them, and are considered to be the closest lifeforms to immortal. They are only vulnerable to alchemy-based attacks, such as Buso Renkin or other homunculi.

Animal-type and Plant-type homunculi possess strength relative to their animal or plant base as well as retaining their sentience (they have the intelligence and reasoning of a human, but consider themselves to be an animal or plant). To activate their abilities, they have to 'transform', usually resulting in a large version of its base (an Eagle-type homunculus would become a giant eagle, for example). Often the homunculi's creator would have to brainwash them into following their creator with blind loyalty, though a few have been known to do so by their own choice.

Human-type homunculi do not change form, but merely gain the strength and regenerative powers of a homunculus while retaining their human form and mind, or at least a humanoid shape (as the embryo for a human homunculus almost always comes from the human him/herself). Human-type homunculi have one distinct advantage over Animal or Plant-types; they have the ability to use Buso Renkin (only humans can use Buso Renkins).

Most homunculi have the urge to eat other humans, but in episode 25 Papillon tells Victoria that eating humans doesn't wet his appetite. Victoria explains that homunculi eat humans because they desire to regain the aspects of humanity that they gave up; this may be why we never hear of Washio, who was once a wild hawk, eating any humans. She then tells Papillon that because he no longer has any connection to humanity (or rather, that he no longer desires to be human), he has become something other than human or homunculus, but rather a "superhuman".

Kazuki Muto

Kazuki Muto (武藤カズキ Mutō Kazuki^?) is a 16-year-old boy who attends Ginsei Private Academy with his younger sister, Mahiro. After becoming involved in Tokiko Tsumura's fight, subsequently being killed by a homunculus, and then revived by a Kakugane, he is told to return to his ordinary life, but instead insists upon assisting Tokiko in her battles. Kazuki is very enthusiastic, friendly and caring for his friends and sister Mahiro; he tends to put himself in difficult situations in order to assist or protect others. Although he has an unusual way of showing it, he does have strong feelings for Tokiko Tsumura. Kazuki has been called a hypocrite on a number of occasions (almost every time by Papillion): such instances being Kazuki's trying to stop Koshaku Chono from becoming a homunculus and having to destroy him, becoming (albeit against his will) a Victor and thus giving up his humanity and (in "Buso Renkin After") trying to apologize to Tokiko for wanting to touch her scar.

The Kakugane, which Tokiko had used to revive Kazuki, turned out to be Black Kakugane III, disguised as a normal Kakugane, which transformed him into a Victor. He is then pursued by the 'Muto-assassination team', as well as his former commander, Captain Bravo. During his assassination, he was dubbed 'Victor III' by the Alchemy Warriors. Afterwards he was given his freedom as he had promised to destroy himself if he could not find a cure for the Victor transformation before six weeks (the amount of time it takes the Black Kakugane to permanently change him into his Victor form). In the end, he sacrifices himself when he sends himself and Victor to the moon with Sunlight Heart+. In Buso Renkin Period, however, he returns to Earth successfully with help from Victor's Buso Renkin, Fatal Attraction. As soon as he returned to Earth, he and Papillon settled their scores, with Kazuki claiming victory. After this, he returns to a normal life with Tokiko, Mahiro and his friends (despite his image being used as part of a fast-food promotion under the name "Hypocrite Boy").

His Buso Renkin is Sunlight Heart (+) (サンライト・ハート Sanraito Hāto^?). It first was believed to be Kakugane LXX, but Kazuki came to discover he was actually in possession of the Black Kakugane III, with the actual Kakugane LXX being in the possession of Dr. Butterfly. Seeing as the Kakugane doubles as his heart, his Buso Renkin plays a unique and critical role in Kazuki's survival. Once invoked, his Buso Renkin, Sunlight Heart, takes the form of a spear-lance with a large decorative cloth attached. He was told his personality fit as a spear, so his Kakugane took that form. The cloth is turned into an energy force when it resonates with Kazuki's willpower. The cloth's energy can be used as propulsive kinetic energy for forward charging, or, dissipating the gravitational forces of a fall. This ability is the origin of its name "Sunlight", as the light it radiates shines like the rays of the sun.

As the story progresses, Sunlight Heart changes into Sunlight Heart+, with a smaller, sleeker design. This new streamlined version, at first glance, seems inadequate as a lance due to its decreased reach and size. However, Sunlight Heart+'s true properties reveal themselves as being able to vastly increase its reach and power; responding to Kazuki's willpower to unleash its self-contained energy, disassembling into, and arranging its core components in the most efficient formations. To this extent, it activates its alchemic powers in the same manner as the original Sunlight Heart. Though lacking the cloth, it can generate propulsive forces from the point at the end of the handle (which is shaped like the original Sunlight Heart, though much smaller) which opens to release kinetic energy. It can also fire off blasts of internal energy.

Sunlight Heart+ is last seen in Buso Renkin Period, when it was destroyed by Papillon's Buso Renkin, Near-Death Happiness, with only the original spear's head remaining; however since it is seen that Buso Renkin regenerate as time passes, Sunlight Heart would have been repaired. Unlike most of the other Kakugane, which had been collected and hidden away when the Alchemist Warriors suspended operations, Kazuki was allowed to keep his since he cannot survive without it.

Kazuki adopts the habit of naming certain attacks. His most frequently used are:

• Sunlight Slasher: (formerly named the "Jousting Slasher") is a straight charge attack under the propulsion of cloth's energy at full capacity.
• Sunlight Flasher: (formerly the "Jousting Flasher") uses a burst of bright light from the cloth to blind the enemy.
• Sunlight Crasher: (formerly the "Jousting Crasher") is his strongest attack, which wraps the cloth around the lance and uses its energy force to increase the overall speed and destructive force of the charge.

Watsuki Nobuhiro states that Kazuki's initial design and personality was based on Makimachi Misao from Rurouni Kenshin, adding that his hair tips are reminiscent of Misao's hairstyle.

Voiced by: Jun Fukuyama (Japanese), Steve Staley (English)

Koshaku Chono

Koushaku Chono (蝶野攻爵 Chōno Kōshaku^?), better known as Papillon in the series, is a 19-year-old genius student from Kazuki's school and was meant to be heir to the Chono family fortune. However, he is also deathly ill and has had to repeat several years of school, due to the amount of time he has needed to spend in the hospital, and was disinherited by his strict-ideal father. Upon discovering a 100-year-old research diary from his great-great-grandfather, he learned ofalchemy and the process of making homunculi, experimenting with various animals first, before turning himself into a human-type homunculus, renaming himself "Papillon" (he pronounces it "Pa-Pil-Lon"). However, he's imperfect, as he was forced to use an unfinished homunculus core to recreate himself (in the original Japanese, it was said that he used his own sick cells to create the core, so the disease remained). He now suffers from the same sickness, but will not die. He began his move by eating every member of his family who could not recognize him as Koshaku, but as his brother Jiro, to the point of even killing his own father and brother. To prevent Papillon from eating more people, Kazuki had no choice but to kill him. After his initial defeat at the hands of Kazuki, he teams up with the homunculus Dr. Butterfly, his still-living great-great-grandfather. After finding out that Dr. Butterfly was just using him, he aids Kazuki and Tokiko, but for his own ends. After defeating butterfly and finding out about Victor, he decides to become another "Victor" after learning that Kazuki became like Victor as well. After the LXE fell, he became a team with Ouka to turn Kazuki back to normal again, in order to duel and kill Kazuki. In the end, he does restore Kazuki to a normal human with the white Kakugane he created himself, and loses the duel. However, Kazuki does not kill him because he already killed him once and thought that he was a good person. He then becomes one of the many urban legends in Japan, nicknamed 'Butterfly Man Papillon', where he is now loved by all of the people in the city, becomes friendly with everyone, and even has a promotion deal with the local fast-food restaurant. Like Kazuki, Papillon was seen with his Buso Renkin at the end of the anime and manga, which can imply that he was allowed to keep his Kakugane (though he may have just made a new one).

As Papillon, he is flamboyant and reckless. He appears in public wearing his mask and in revealing or outlandish outfits, apparently oblivious to or possibly enjoying the stares of bystanders(to the point that he even refers to himself as a pervert). He also slowly loses a thirst to eat human and his wish to burn the world to the ground, slowly becoming something more than a homunculus with Victoria Powered referring him as "superhuman". After Kazuki was thought to have died by the hands of Victor on the moon, he claims the world is trash without him. He deems Kazuki the only human who is worthy of calling him by his original name as Kazuki believes humans can have power without sacrificing their humanity which is something Chouno is trying to disprove, and enjoys referring to Kazuki as a "hypocrite". The majority of the series his relationship with Kazuki is portrayed comically.

His Buso Renkin is Kakugane LXI, Near-Death Happiness (ニアデス・ハピネス Niadesu Hapinesu^?). When activated it appears as black gunpowder that typically takes the form of a pair of butterfly wings on his back. He also can create a number of small butterflies from it that explode on impact and that he can use offensively or create a large butterfly which he can ride on. When all of the butterflies are used up, it takes three days to regenerate. When first activated, Papillon suffers a shock which he seems to enjoy, saying he "forgot the ecstasy of near-death".

Voiced by: Mitsuaki Madono (Japanese), Spike Spencer (English)