Buso Renkin (Japanese: 武装錬金, Hepburn: Busō Renkin; lit. transl. "Alchemical Weapons") is a Japanese manga series written and illustrated by Nobuhiro Watsuki. It was serialized in publisher Shueisha's shōnen manga magazine Weekly Shōnen Jump magazine from June 2003 to April 2005. The individual chapters were republished by Shueisha in ten tankōbon (bound volumes). It follows Kazuki Muto, who becomes an alchemical warrior in the battle against alchemical monsters known as homunculi. Watsuki envisioned the manga as his last shōnen manga, and then he tried to do as much as he could with that genre. The series has been licensed by Viz Media for North American release.

The manga has been adapted into an anime television series, which was produced by studio Xebec and was broadcast on Japanese television network TV Tokyo from 2006 to 2007. In December 2007, the anime was announced for North American DVD release by Viz Media. In 2009, the series made its American television debut on the Funimation Channel, with American broadcast rights acquired by Funimation from Viz Media. The series has also spawned two drama CDs, two light novels, a PlayStation 2 video game, and many types of Buso Renkin-themed merchandise.

In Japan, the Buso Renkin manga has sold over 3 million volumes and was nominated for the science fiction works focused Seiun Award. It received a mixed reception from manga and anime publications. Watsuki's art received the most positive comments from reviewers, while other aspects of the manga, such as its action and characters, have divided critics' opinions. The anime, which critics described as a generic shōnen fighting series, received mostly negative reception.

The series follows Kazuki Muto, who saves Tokiko Tsumura and is killed by an alchemical monster known as a homunculus. Tokiko, an alchemist warrior, feels responsible and revives him by replacing his destroyed heart with a kakugane (核鉄). The kakugane is an alchemical device which, when activated, takes a weapon form based on its user's personality, forming a buso renkin—the only thing that can destroy a homunculus. Kazuki creates his own buso renkin and joins Tokiko in the fight against the homunculi and their master, Koushaku Chouno. Chouno, who has renamed himself "Papillon", is killed by Kazuki, but is later resurrected by the L.X.E., a humanoid homunculi group led by Chouno's great-great-grandfather Bakushaku Chouno, now calling himself Dr. Butterfly. In various battles, Kazuki, Tokiko and Captain Bravo (their team leader) destroy most of the L.X.E.'s members. After learning that Dr. Butterfly believes him to be weak and useless, Papillon rebels against the L.X.E. and kills Dr. Butterfly.

Before his death, Dr. Butterfly drains the energy of the students at Kazuki's school to heal and revive Victor, a being superior to humans and homunculi. Victor is confronted by Kazuki, but Victor is not interested in fighting and leaves. During the battle, however, Kazuki's kakugane is revealed to be the same type as the Victor's—a black kakugane created by the Alchemist Army as a prototype to the philosopher's stone. The black kakugane absorbs human life forces; to prevent this from happening, Kazuki's death is ordered by the Alchemist Army. Captain Bravo tries to kill Kazuki, but Tokiko finds him alive. A team is commissioned to confirm Kazuki's death, but Kazuki, Tokiko and Gouta Nakamura (an Alchemist Warrior and former protégé of Tokiko's) fight their way past the members of the Re-Extermination Squad. Later, Kazuki's death is postponed because, as the Alchemists' leader explains, their top priority is to defeat Victor.

Kazuki and Tokiko find the white kakugane, which can negate the effects of the black kakugane and is guarded by Victor's daughter Victoria, who is herself a humanoid homunculus. During the Alchemist Army's final battle against Victor, Kazuki applies the white kakugane to Victor, but it only weakens him. To protect humankind from both of them, Kazuki propels himself and Victor to the moon. Later, Papillion creates a white kakugane to heal Kazuki. The Alchemist Army rescues Kazuki, creates another white kakugane and restores Victor's humanity. Reunited with his daughter, Victor asks the Alchemist Army to turn him into a homunculus and tells them that he and his daughter will lead all the homunculi to the moon. The Alchemist Army dedicates itself to research a way to revert homunculi back into humans, ending their war activities. All Warriors abdicate their kakugane. Kazuki and Tokiko return to their daily lives together while Papillon becomes an urban legend throughout Japan.

Nobuhiro Watsuki started writing Buso Renkin thinking it would be his last shōnen manga; he tried to do "everything [he] ever wanted" with that genre. He unexpectedly experienced problems drawing the manga's fight scenes and said he "struggled with the comedic elements". Watsuki drew references from several sources in Buso Renkin; from his past works Rurouni Kenshin and Gun Blaze West to American comics, and from films to other anime and manga. Despite dealing with alchemy, Watsuki initially avoided mentioning the philosopher's stone because he thought he could be accused of plagiarizing another series. He could not omit mentioning it, but he said that it is "general knowledge". During the series' publication, Watsuki had four severe colds; the fourth cold made him so weak that he could not finish the chapter he was due to send to Weekly Shōnen Jump.

The chapters of Buso Renkin were written and illustrated by Nobuhiro Watsuki and were serialized in Shueisha's shōnen magazine Weekly Shōnen Jump from June 23, 2003, to April 25, 2005. The first 79 chapters were serialized in Weekly Shōnen Jump; the final chapter was published in another magazine from Shueisha in two installments. Shueisha published the individual chapters in a series of ten tankōbon (collected volumes), which were released between January 5, 2004, and April 4, 2006.