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

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

During the violent upheaval of the Bakumatsu era, Hitokiri Battosai was a feared and ruthless assassin. But now that the Meiji Restoration has begun to heal the wounds of civil war, Battosai has taken up a new name...and a new calling! He is now Himura Kenshin , a rurouni wanderer who has vowed to only draw his sword to protect those in need. But not everyone is pleased with Kenshin’s new direction, and enemies from his dark past have vowed to bring him down! -- VIZ Media

Kazuki Mutou is mortally wounded saving a girl from a strange monster, but is given a new life through the power of the alchemically-made Core Iron. Along with a second chance, this grants him the ability to use his own Buso Renkin, or Alchemy Weapon. Joining forces with Tokiko, the Buso Renkin user he'd saved earlier and who gave him the Core Iron, he uses his newfound powers to fight the malevolent Homunculus monsters and protect his friends and the rest of mankind.

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

High school students heroic act turns into epic human vs. monster sword fight! Buso Renkin is the story of teenager Kazuki Muto, who dies trying to save a girl who was being attacked by an eerie monster. The next morning, however, Kazuki is left wondering whether it was all a dream. Lo and behold, the girl, the monster, and his death are all real! The girl, Tokiko Tsumura, was actually trying to slay the homunculus (a beast that can take the form of humans, and whose main source of food is people), but Kazuki got in her way. To revive Kazuki, Tokiko replaces his heart with a "kakugane," an alchemic device that allows him to summon a lance with which to fight the monsters. It turns out that Tokiko is a member of the Alchemist Warriors, an organization sworn to protect the world from the diabolical creatures. Soon, Kazuki joins Tokiko in her quest to terminate the sinister being that creates and controls the homunculus. 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?