Madlax (マドラックス, Madorakkusu) is a 26-episode Japanese anime television series produced in 2004 by the Bee Train animation studio. Kōichi Mashimo directed Madlax and the soundtrack was composed by Yuki Kajiura. The DVD version was released by ADV Films in North America and the United Kingdom and by Madman Entertainment in Australia and New Zealand.

The story revolves around the two young women Margaret and Madlax, who seemingly have little in common and do not know of the other's existence at the beginning. Madlax is a legendary mercenary and assassin in the fictional civil war-torn country of Gazth-Sonika, who cannot remember her past or indeed her real name before twelve years ago, when the war started. The other main character is Margaret Burton, the sole heir of a wealthy aristocratic family in the peaceful European country Nafrece. Twelve years before the story begins, an airliner Margaret and her mother were on crashed over Gazth-Sonika, and its passengers, as well as Margaret's father who led the rescuers, have been missing ever since. Margaret, however, mysteriously traveled back to Nafrece on her own, losing her memories prior to her return; the only thing she recalls is a single word, "Madlax". With this thread linking the two girls, they both independently start investigating the powerful crime syndicate Enfant after its enigmatic mastermind shows interest in both of them.

Madlax was produced as a spiritual successor to the studio's earlier project, Noir, and together with El Cazador de la Bruja, these series constitute a trilogy exploring the "girls-with-guns" genre. The production of Madlax began in 2002 but it wasn't until Yōsuke Kuroda joined the project that the series took its final form. While the critics noted the resulting similarities between Noir and Madlax, they also acknowledged the differences, such as the latter's less episodic and more plot-driven style and, in particular contrast to the predominantly realistic Noir, incorporation of many supernatural elements, which the audience must often interpret without further explanation.

The first half of the series alternates between the two leads. Madlax is one of the most efficient special ops agents for hire in the war-torn Gazth-Sonika, while Margaret Burton is a sleepy, clumsy amnesiac living in Nafrece, a country styled after France. When a "picture book", presumably given to Margaret by her late father, attracts the attention of international criminal network Enfant, she discovers that the origins of the book lie in Gazth-Sonika. Enfant's top operative, Carrossea Doon, tracks Margaret down but tips off his superiors in the wrong direction, towards Madlax, who has been causing Enfant trouble for some time. Meanwhile, Vanessa Rene, Margaret's former tutor whose parents died because of Gazth-Sonikan war, discovers that her current employer, Bookwald Industries, covertly supports the war by supplying both sides with firearms and starts investigating its true cause. Her investigation brings her to Gazth-Sonika, where Madlax is hired as her bodyguard, and together, they uncover data that proves Enfant orchestrated the entire conflict. Enfant eventually intercepts them and they are forced into hiding. Back in Nafrece, Margaret decides to help Vanessa and travels to Gazth-Sonika, accompanied by her devoted and sometimes overprotective maid Elenore Baker and Carrossea Doon.

Eventually, Madlax and Margaret meet and embark on a search for Quanzitta Marison, a Gazth-Sonikan mystic who supposedly knows about Margaret's book, Enfant's involvement with it, and Enfant itself. Lady Quanzitta does indeed tell them about Enfant and its plans to plunge the entire world into a total war, starting with Gazth-Sonika. She reveals that Enfant's leader Friday Monday possesses supernatural powers connected to the three ancient books, one of which belongs to Margaret. Margaret uses her own supernatural abilities and that of her book to return her lost memories. Carrossea, who has been aiding Margaret, requests that his memories be restored as well despite warnings not to do so; he discovers that he, in fact, died 12 years ago and held on to life only by sheer force of will to protect Margaret. Carrossea disappears, and Margaret is captured by Monday who intends to use her abilities to advance his own plans.

While Margaret and Carrossea perform the ritual, Madlax is attacked by Limelda Jorg, a Gazth-Sonikan sniper who holds a grudge against Madlax ever since she failed to stop an assassination by Madlax earlier in the show. Limelda kills Vanessa while targeting Madlax, sending the latter into clinical depression. Elenore and Lady Quanzitta's servant Nakhl manage to restore Madlax's will to live and persuade her to save Margaret, and the three storm Enfant's headquarters together. During the assault, Elenore is killed and Margaret, now under Monday's control, shoots Madlax.

Believing Madlax to be dead, Monday commences a ritual to unleash people's inhibitions and trigger worldwide anarchy; but Margaret's memories return and she snaps out of his mind control. Only now does the audience learn the back-story: back in 1999, Monday drove Margaret's father insane with his powers and she was forced to kill her own father. To escape the horrible truth of her patricide, Margaret split herself into three personae: the "memory keeper" Laetitia, the sinful Madlax, and the innocent Margaret herself. Margaret then fuses her three personae back together to undo the ritual she previously performed with Monday, saving the world from insanity. Madlax, who should no longer exist after the fusion, appears and guns down Monday. It becomes apparent that Margaret has once again split herself into three, judging that after twelve years, she no longer has the right to make decisions for her other personae.

When everything is said and done, Margaret fully releases Madlax so she can live her life freely and also adopts Laetitia as her younger sister so she won't be alone. Madlax ultimately makes peace with Limelda and they travel together.