A DLC arround the Black Sea: Armenians, Georgians, Vlachs, and renaming Slavs to Rus, simple and beautiful.
If we really, realy need a South Slavic civilization other than the Bulgarians, then the Croatians are really good because their naval indentity is rare in that region. And this can give the DLC a good title: Antemurae Christianitatis, to symbolize the history of these civilizations fighting against the invasion of Muslim power.
PS. Even if there will be no Croatians, the DLC still can be simply named Bulwark of Christendom.
In fairy tails we can often see bogatyrs who are an unreal super-verison of vityazes. Bogatyr means smth like “rich one” but rich with force, not money.
Bogatyr derives from the Turkic word Baghatur, meaning hero
Bogatyrs like Alyosha Popovich, Dobrynya Nikitich, Svyatogor, Ilya Muromets, were folk heroes akin to Hercules, Odysseus, and Theseus from the Greek myths