Okay MakaYuri fans. Imagine this:
It's the middle of the zombie apocalypse. Yuri and Makarov are the only ones who survived out of the entire Inner Circle
Makarov, being the asshole that he is, makes Yuri do most of the work around camp and during supply runs....but a small part of him also does this as an excuse to watch over Yuri. To protect him from any undead or raiders that may ambush them
While out on a particular supply run, Yuri accidentally makes too much noise and draws the attention of a nearby horde while the duo are in an old pharmacy looking for medicine.
Makarov creates a distraction for Yuri, so Yuri can escape...but the two end up getting separated. Yuri doesn't realize this until he's back at camp, and of course, starts to freak out a little.
When Yuri goes back to search for Makarov, he sees the horde has moved on but numerous dead zombies litter the pharmacy grounds....with a bitten and already turned Makarov sitting on the ground near the front counter.
Yuri being Yuri, couldn't bring himself to finish off his close friend. Yuri, being so naive, thinks that he could find a cure to help Makarov. So he carefully immobilizes his zombified friend and makes it to where he can't bite him. (Breaks his jaws, gags him, muzzles him....I'll let you decide)
Months pass with no luck in finding a cure. Yuri has practically given up at this point but still chooses not to kill Makarov. Mostly because of how guilty he feels about the situation. He knows it's his fault; that if he wasn't so loud in the pharmacy, that horde wouldn't have come and Makarov wouldn't have been bitten.
Yuri is basically keeping Makarov as a physical reminder of his guilt and shame now, of how he got his closest friend killed...of how he failed his friend.
He uses Makarov to vent a lot now too. Something he really couldn't do when Makarov was alive considering how cold and callous the former terrorist was. I mean, it's not like he can even understand him now anyways....right?
As Yuri vents to the zombified Makarov one night, something about how he was starting to have doubts about the attack they were planning right before the world went to shit....about how he was this close to turning Makarov in to the FSB. The only response Yuri gets is the usual rugged, horase groans and grunts from Makarov.
He gets up, about to head over to his sleeping bag to turn in for the night after he was finished ranting when something catches his attention. He stops and listens out for it....and again, he hears it. Turning back to Makarov, Yuri's blue eyes meet his clouded grey ones just as Makarov's mouth moves again....
Yuri nearly collapses right then and there as his undead friend utters that single word. His nickname that only Makarov used for him. Makarov was still in that husk....somewhere....