Based on Ekaterina Kurae's chapter 16 from the manga, and episode 10.5 of the anime.

When Tomo Yamanobe's father—the former headmaster of Saint Mikhailov Academy—disappeared, he left nothing behind except for a piece of art called the icon. Soon after his disappearance, rumors of a serial killer attacking female students of the academy began to spread. As Tomo and her sister Mafuyu Oribe head home after being tormented at school, Tomo trips over an injured silver-haired boy who abruptly vanishes while being tended to. Mafuyu goes to look for him, only to discover that the church holding the icon is burning down. When she tries to save the painting, the rumored serial killer suddenly attacks her with a mysterious ability to control magnesium. Appearing out of nowhere, the silver-haired boy, who can control iron, rescues Mafuyu. Mafuyu finds out that the boy, named Alexander Nikolaevich Sasha Hell, is a qwaser—a being who is capable of controlling an element through the power of soma, received through the act of breastfeeding. Confused by the ordeal, Mafuyu attempts to move past it with little luck, as Sasha transfers to her class the next day. What will become of Tomo and Mafuyu's normal school life with the danger of other qwasers looming close to them?

Sasha is partnered with Hana as his new Maria. They infiltrate an all-girls academy, forcing Sasha to crossdress, in search of a Qwaser-related artifact called the Magdalena of Thunder which has appeared in one of the students. However, they have some competition in their search of it. (Source: ANN)

At the beginning of the Edo Era, when people enjoyed a time of peace, Lord Tokugawa Tadanaga holds a fighting tournament. In the past, matches were fought with wooden swords. This time, real swords will be used. One-armed Fujiki Gennosuke and blind Irako Seigen will fight each other in this match. Both are disciples of Iwamoto Kogan, who is known as Japan's greatest swordsman. Each of them are determined to prove himself the successor of Iwamoto's school. However, there can only be one champion. So begins a story of intertwining fates, conflict, and strange destinies. (Source: ANN)