[Yoimiya's asking the right questions and it reminds him that he has to try to cool down a little bit and think. Who would try to hurt him through a woman he's having relations with? Why would they be mad at him, and how would they even know who to be mad at?]

I'm pretty thorough when it comes to my job, [he begins slowly, fighting down his rage and trying to see it from more of an analytical state of mind.]

So I find it hard to believe that any singular person that I've wronged would be specifically angry at me. They shouldn't even know who I am. But, I'm also the one who gets sent out to do the dirty work, so one could single it all down to me. That letter mentioned Nizhnii by name, so that means that they have some kind of inkling behind the real purpose of the company.

[He sighs as he lands on what he thinks is the answer here, and he doesn't like it.]

This is most likely bigger than it seems. They can't get to my family, so they've just found the next best thing to get to me and my employer...you. "They" being a rival of ours.