Background(for those of you who dont know what buso renkin is)

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 be 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 a Kakugane 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.


[edit] 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.


[edit] 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 Kaguganes. 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.


[edit] 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 crushes the brain and takes control of the body, giving it abilities that mimic the natural talents of the embryo's origin.

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 whet 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".