Maybe the point was cleared before and I forgot, but since they’re married, shouldn’t their workplace know about their relationship already ? How can they still hide it ?
Well, actually they not 100% hide it. All workers at their own departement know that Hara and Fuyuki are married (except that one black short hair female the writer, I was forgot her name). But they don't know who married to who. Also, Fuyuki always have a lot of excuses. Like some early chapter (I was forgot which chapter) they caught together when go to the date but Fuyuki came with the excuse "for work reference and they both (Hara and Fuyuki) are the departement leader".
Well, just like someone replied earlier. The boss is the only person that know about their marriage and he gave them special treatment because Hara and Fuyuki is the important people at their workplace. And if you think about it, at their workplace they still use different surename even tho they already married. And Hara actually is the surename. The guy first name is Taiyo if I remember correctly. Taiyo Hara and Fuyuki Toujo -> Fuyuki Hara (technically).