at sabantuy, various types of games are played there and one of them is a game where you have to take a coin out of a bowl filled with qatiq (a fermented milk product similar to yogurt) without using your hands. which means you have to dip your face in the bowl and use your mouth to find the coin and take it out.
in medieval times, volga bulgaria and the rus' principalities were often raiding each other or in war with each other, but there were times where they'd trade with each other and help each other (such as volga bulgaria sending them wheat when there was famine in the rus' principalities)
so I guess in hetalia, volga bulgaria and russia were something like childhood friends? that'd fight sometimes? but then still be good friends?
here's what i'm imagining:
volga bulgaria has invited russia to sabantuy so they can celebrate together and he shows him various fun stuff around
volga bulgaria: now this is a bowl of qatiq, here's a coin, you have to take it out of the bowl using your mouth, here, let me show you how *dips face into the bowl*
russia: woah sounds fun I'll help you find it : ) *pushes volga bulgaria's head deeper into the bowl*
volga bulgaria: *begins shifting and squirming*
russia: oh did you find it? seems like you haven't yet *keeps on pressing on his head*
volga bulgaria begins to struggle more and more as he can't take a breath. soon, he starts thrashing desperately. as a last resort, he grabs onto russia's wrists, attempting to pull them away from his head, but to no avail.
russia: oh you must've found it *stops pressing volga bulgaria's head into the bowl*
he's too late though. volga bulgaria suddenly stops moving, his body going limp
russia: *pulls him away from the bowl* awww you didn't find it… *prepares to dip his face into the bowl again, but suddenly stops*
russia: friend? are you upset at me? why aren't you talking to me? sorry if I've said something that has offended you
russia: aww you must be really tired, falling asleep like that. or is finding a coin in qatiq much more tiresome than it looks? let's clean your face and move you over there so you can get some sleep : )