Soshite Koyoi wa Kimi ni You

From Shoujo Addiction:
Koga Nana is the new office worker who's really terrible at this kind of work. Since she's always making mistakes, she feels down more often than not. But she keeps on working hard because of Shibano-kaichou <3
One day, they go out for dinner together, but it turns out that Shibano can't hold his drink, and he gets drunk after just one glass of beer. With no other choice, Nana can only take him home with her.
What'll happen next—?