Battle at Yekaterinburg ("Kessen· ekaterinburuku", 決戦・エカテリンブルク) is the tenth episode in the anime adaption of World Break: Aria of Curse for a Holy Swordsman. It first aired on March 15th, 2015.
In his slumber, Moroha is having a nightmare about tragedy that befalls upon his past life. While awaken from the nightmare, Moroha find himself slept with AJ who is naked because she treated his with her healing powers. It turns out that while Moroha receiving a thunder strike from Vasilisa, AJ, who broke the mirror that forced the hooded assassin escaped, tried to reach Moroha and get him into safety. While lamenting about his "idiocy" for saving her despite igniting a war against Russia himself, AJ took Moroha into the nearby hut. After seeing a severed injured Moroha, AJ had to heal him for the entire night.
On the next day, Moroha and AJ are visited by Katya, a Russian Savior whom Moroha fought the previous night, asking Moroha to rescue her friend Yuli from Vasilisa. During their journey for Yekaterinburg, Moroha and AJ learn from Katya that because most of the Russian Saviors didn't have any families, they had to comply to Vasilisa's command without questioning her motive, and most of them served as her personal bodyguards. Nevertheless, in order not to drag the girls into his battle against the Lightning Empress herself (for AJ case, he didn't wishes to confront Edward should AJ met any mishaps), Moroha decides to attack Yekaterinburg alone.
Elsewhere, Darco reports to his supervisor about the battle whilst revealing Moroha's weakness: his mercy and selflessness, though he is still purged Vasilisa due to his failure for unable to kill Moroha. To her surprise, Vasilisa sees Moroha from afar and decides to give her a "welcoming greeting" by summoning her Cruel Crusaders to attack her guest. Despite outnumbered by more monsters before reaching to Vasilisa's palace, Moroha manages to defeat most of them until his confrontation with all Russian Saviors in the battlefield, with some unwillingly attack Moroha while others remain loyal to their queen. Just as Moroha is pinned by Yuli's gravity powers, which gives the Russian Saviors an opening in attacking Moroha, AJ, Katya, Satsuki and Shizuno arrive timely for their rescue.
While Vasilisa is amused as she watches Moroha's and his friends's struggle, Leshya is next to arrive as she convinces her Russian compatriots to be "reborn" as a person while revolting against the Lightning Empress. After Yuli is freed from the necklace's control, all Russian Saviors join Moroha's battle against the Vasilisa. While telling her agents that Yekaterinburg is going to be destroyed, Vasilisa decides to put an end towards Moroha by summoning a lightning giant via her song. Initially being overwhelmed by its power, Moroha uses Ouroboros to flood the entire area while using the water to defeat the monster, resulting Vasilisa's defeat. Even deserted by her own men while cornered by Moroha, the Lightning Empress made her last attempt to beat Moroha with a lighting strike, only to be absorbed by Moroha's Ouroboros instead. Feared for her life, Vasilisa pleas Moroha to spare her as she unwilling to lose her precious possession, which angered Moroha as he berated the fallen Lightning Empress to stop taking away someone's precious item away before leaving her palace. With Moroha's departure, Vasilisa admits her defeat and the battle resulted Moroha's victory.
(Numbers indicate order of appearance.)