Talk about being at the wrong place at the wrong time! High school student Kazuki Muto had no clue what he was in for when he rescued damsel in distress Tokiko from a monster known as a "homunculus." Disguised as humans--who actually eat humans--homunculi are malevolent creatures that affix themselves to people's brains, and once fully grown, the only thing that can annihilate them is a weapon called Buso Renkin! Follow the adventures of Kazuki after he discovers that it was actually Tokiko who saved his life by implanting a kakugane--an alchemical device that transforms into a buso renkin--to replace his heart! -- VIZ Media

Kazuki inadvertently reveals his identity as an Alchemist Warrior to the Hayasaka twins, members of the L.X.E. (League of Extraordinary Elects), when he activates his Buso Renkin in front of them. After Tokiko and Kazuki take on the twins in a late-night battle, they learn the location of the L.X.E. headquarters, and head there along with Captain Bravo. Intending to put an end to Dr. Butterfly's organization, they discover that yet another evil plan has been set in motion... -- VIZ Media

Kazuki's black kakugane, which powers his Buso Renkin weapon and keeps him alive, will soon advance to the point where it begins draining life from others around him. Teaming up with his partner Tokiko, Kazuki leaves on a mission to find out more about the black kakugane in hopes of keeping this from happening. Meanwhile they encounter an elite group of Alchemist Warriors that have been assigned to hunt them down and kill them! -- VIZ Media

Never underestimate the power of underwear! With no battle gear to speak of besides his butterfly mask and skivvies, Papillon Mask survives a bitter duel against our boy Kazuki. Meanwhile, Papillon Mask's great-great-grandfather Dr. Butterfly promises him the true powers of a humanoid homunculus, which includes the ability to use a Buso Renkin. Will Kazuki and Tokiko be able to fend off their very powerful--and eccentric--nemesis? -- VIZ Media

Kazuki and Tokiko find themselves face to face with the legendary traitor of the Alchemist Warriors. The traitor, Victor, has a black kakugane for a heart, giving him the ability to drain energy from any humans in the area and increase his own strength. Then Kazuki discovers that he too has a black kakugane inside him. A fierce battle ensues, pitting the two owners of the rare black kakugane against one another! -- VIZ Media

While investigating the mystery of the black kakugane, Kazuki, Tokiko and Gouta unexpectedly meet up with Alexandria and Victoria, the wife and daughter of the traitorous Victor. Alexandria and Victoria explain that a cure for the effects of the black kakugane exists, but it comes with a steep price. Now Kazuki faces a grave choice: Can he afford to pay...or will he find that he can't afford not to? -- VIZ Media

Kazuki and Tokiko are on the run from the hunters of the Alchemist Warriors! Tokiko, now reduced to the size of a doll, fights alongside Kazuki and Gouta as they take on three of the hunters and Captain Bravo himself, whose past is finally revealed! As Kazuki and Captain Bravo's battle draws to a close, another Warrior Chief appears, as well as a man calling himself the Great Warrior Chief. What will it mean for Kazuki and his friends? -- VIZ Media