Alchemy is the mysterious power of which most events of the Buso Renkin series are related to in some way. Sharing several similarities with its classical real-world concept, alchemy is responsible for two major elements in Buso Renkin: homunculus, and "arms alchemy", (Buso Renkin).
In Buso RenkinEdit
While the Buso Renkin universe is shared with that of present day earth, much of the scientific information regarding how alchemy works and achieves its miraculous and magical effects in the series is never divulged. Nevertheless, the science of alchemy in Buso Renkin strives to achieve the common classical goals of real world alchemy: transmutation of lesser metals into gold, creation of a philosopher's stone, and immortality.
A hundred years before the events of Buso Renkin, alchemy was researched secretly, away from the public eye. During this time, the scientists discovered how to synthesize an organism called a homunculus, which later turned out to be a bane to the human race. Homunculus, simply put, are life forms capable of withstanding huge amounts of damage to their bodies, and most have the ability to morph into monstrous forms. Their appearances are based on the type of life-form used in their creation, but all homunculus take on a semi-humanoid form and consciousness. The most frightening quality of these beings is their need to consume humans for sustenance.
Fortunately, a second discovery was made that made homunculus vulnerable: the creation of devices called Kakugane. Appearing as palm-sized hexagonal tablets, a Kakugane contains an alchemic weapon powerful enough to vanquish a homunculus when wielded. Based on the user, kakugane will take the form of a unique offensive or defensive device, called a Buso Renkin: for example, a lance or impenetrable cloak. Each Kakugane draws its strength from the will and instincts of its user. A kakugane is activated by these fighting instincts and can be deactivated at any time afterwards. Kakugane can be utilized by both humans and homunculus, and both are able to weild multiple kakugane. Kakugane are nearly indestructible and they will repair any damage sustained to itself over time, as well as the user - if they are not fatally wounded. Kazuki Muto, the protagonist of the series, is an exception: because his kakugane also serves as his heart, he can withstand far more brutal assaults than a normal human could.
The events of Buso Renkin revolve around the struggle between the homunculi and the organization of kakugane-wielding humans known as the Alchemic Warriors. Therefore, alchemy is primarily featured as a weapon and very little explanation is given beyond its capabilities in battle. Later on, it is revealed that three kakugane known as Black Kakugane exist, which are overwhelmingly powerful and, when replacing a human's heart, will begin to transform the recipient into a monstrous cross between human and homunculous. This process is known as "Victorization", named after the first person to undergo the effects, Victor Powered. The only way to reverse this process is to neutralize the evil with a White Kakugane, which is essentially the polar opposite. These two types become an integral catalyst of the plot in the second half of Buso Renkin.