My business administration teacher told us that in office relationships, there isn't a problem if both participants are in the same "rank", what i mean is that they are not superiors to each other, and that is because neither of them can gain something from the company (favoritism, early promotion, etc.), only from each other (a.k.a. love, wuv, fluff, etc.), i wonder if it works the same way in japan. Of course, it makes for a less exciting story if it isn't Senpai x kouhai.