Aoki Balkanalia蒼きバルカナリア; The Azure Balkanalia

In a Bulgarian village under Ottoman rule during the 16th century, a young girl named Luca endures a life of mistreatment at the hands of her adoptive family, finding her only refuge under the protection of her adoptive brother, Lev. However, one day, soldiers from the Imperial army arrive on a hunt for young boysand Lev is taken away. Thus begins the fateful tale of two souls, bound by a solemn vow to reunite! (Source: Akita Shoten, translated)