Y'all I think the story is like this....
In the past muni(who was the servant) liked the young master but the young master didn't like him back, so now after years later he is trying to get his love( the young master's) but he is too old, so he needs someone else's body, this is were the office guy aka our main character comes, his name is also muni, let's call him muni number 2, so muni number 1 is using muni number 2 to get the young master's love, because that's the only way he can finally be at peace and die. I also think that the boss is the young master but in the modern times, I'm not sure tho.
Let us live, for we must die.