I think there’s more of a philosophical disagreement between you two about what makes a given word “Japanese” and how orthographic renderings are determinative

I think there’s more of a philosophical disagreement between you two about what makes a given word “Japanese” and how orthographic renderings are determinative of that. You highlight lossiness of many loan words and I personally think that when they’ve reached this level of divergence in Japanese, they become equivalent, regardless of orthography (because the Japanese writing system contains within it Roman script). Are “naive,” “ナイーブ,” and “ｎａｉーｂｕ” all Japanese words for example? I don’t think it’s a settled question one way or the other, but is highly variable on context and history. For example, there have been several pushes, beginning with the Meiji to Revolution, to switch Japan to writing exclusively in romaji. If any had succeeded, we’d view this debate quite differently: https://www.jstor.org/stable/27756125?seq=1 https://www.jstor.org/stable/27756125?seq=1