I encountered the word 「鏡越し」 while I'm reading a web novel, titled 『とある殉教者の訃報』by 鼠色猫/長月達平
Here is the full sentence.
「もし、これが鏡越しの会話じゃなかったら、今頃、君はバラバラだったよ。そうならなかったことを、僕に感謝した方がいいんじゃないかな」
I googled 「鏡越し」 and still I couldn't find the meaning of this word. The closet meaning I got when I used google translate was "Glanced up from glasses" and I don't think it is the right translation for this sentence. How should it be translated? Thank you in advance for your help.