|Demon Sword Arc|
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The Demon Sword Arc is the third major story arc in the Soul Eater series. It is also begins the main plot of the series. Maka Albarn and Soul Eater face off against the powerful Demon Sword Ragnarok and his meister Crona, resulting in a horrific loss that shatters the confidence of the meister-weapon pair. Meanwhile, a witch has begun hatching a plan to take down the DWMA. Later, Spirit Albarn explains to Maka the origins of the Kishin, and Black☆Star and Death the Kid attempt to find the Holy Sword, a powerful demon weapon of legends.
Main article: Chapter 4
Maka and Soul complete a mission in Italy but are distracted by the presence of an odd Soul Wavelength amidst numerous human Wavelengths in the nearby Santa Mario Novella Basilica. Maka decides to investigate, discovering the humans have disappeared but the combined Soul Wavelengths of meister and weapon, belonging to Crona, who has within themselves the Demon Sword Ragnarok and controlled by their witch mother, who flies over Santa Mario.
Maka engages Crona in battle, but Ragnarok manages to slice into Soul's weapon form, actually drawing blood. Maka is backed against the front doors of Santa Mario, refusing to block against Ragnarok and thereby risk Soul's life. As Crona throws down Ragnarok for the fatal blow, Soul reverts to his human form, receiving the blow across his chest, spilling his blood and causing him to collapse, nearly dead, at Maka's feet.
Main article: Chapter 5
Maka falls down towards Soul, holding him as Crona prepares to kill them. Suddenly, the blade of Spirit Albarn splinters through the doors of Santa Mario, wielded by Franken Stein. As Crona and Stein fight, Maka can only watch.
After Stein tosses Crona out of Santa Mario, they begin to reject the Black Blood within their body. Before Stein can retrieve Crona to take back with them to the Academy, the witch hovering over them sends down a snake to attack Stein and escape with Crona. Rather than pursue the witch, Stein decides to bring Soul back home for medical attention.
Stein performs surgery on Soul, managing to save his life. But as he reveals to Spirit, Crona's Black Blood has now infected Soul. While Maka, Black☆Star, and Tsubaki Nakatsukasa look upon the unconscious Soul, they are interrupted by the arrival of the Academy's physician, Dr. Medusa, who will tend to his treatment. After giving Maka words of encouragement, she turns away from her, revealing a serpentine face and tongue: she was the witch who observed Maka and Stein's battle in Italy, the mother of Crona, the snake witch Medusa Gorgon.
Main article: Chapter 6
Soul struggles to recover from Crona's attack, suffering from nightmares and worried how to respond to his despondent meister Maka. Spirit visits Maka to try to cheer her up, while she is more interested in knowing what threat Soul faces from his injuries. Spirit explains that Ragnarok risks becoming a Kishin, but he keeps to himself his own fears that Soul could become a Kishin, too.
Meanwhile, Sid assigns Black☆Star to clean the Academy's library, as punishment for his inability to acquire any souls. While in the library, Black☆Star is joined by Death the Kid, who shows him a book about the powerful Holy Sword, Excalibur. After having Tsubaki take over cleaning duties for him, Black☆Star joins Kid in the British Isles to search the Eternal Cave and find Excalibur--who is revealed to be an annoying, conceited windbag. Despite Excalibur's offer to be weapon to both Black☆Star and Kid, the two meisters depart--only to find that Excalibur has left an embarrassing thank-you gift at the Academy promising to be waiting for the two.