This series isn't very well identified in terms of volumes, so it's difficult to tell what is what in the bookstore, other than that this omnibus is clearly a thicker volume than the other book. Otherwise, the covers and title all remain the same for the other versions that were physically in stock, adding to the confusion.
Ryo and Zen were rivals clear back to their high school days. What Zen didn't know was that Ryo was pinning for him even back then. It takes their first trip together for Ryo to learn that Zen may have been waiting for him to call even back then. It's amusing how these two are so close and are often the spotlights of office gossip, and yet somehow they manage to stay entirely under the radar. At least one person in the office is in the know, but only after causing a lot of trouble and being told outright. It seems in general, the office thinks that even if the boys have mellowed, they would never get along, even if they were married. Interesting given their personal contests seem to be how they thrive and communicate with each other. It's also interesting to see how they deal with trust and jealousy issues, which are typically even more common when your relationship is hidden. For all of Zen's complaining, it would seem that at least when they are together, their physical relationship is more than healthy. In that regard, their future plans could either go really well or really wrong given their schedules and how quickly they tend to fall together.