I'm falling in love - LenaMiu

Miu and Lena are coworkers who can't go a second without arguing, you could say they're office rivals. Miu keeps pressuring her, she wants Lena to lose her temper, no one can be that calm, it's irritating. Lena, for her part just wants Miu to shut up, even for a second, just long enough for Lena to hear her own thoughts.
Their biggest problem isn't figuring out how they got to that point, it's understanding how they ended up longing for each other. Who fell first? How did they go from yelling at each other about who uses the printer first to kissing against it?