Fujii Kaze Musical Genius

To preface, Fujii Kaze is a contemporary Japanese pop music composer who has quite the following from his home country and abroad as well. His songs range from classic love songs, to a faulty nostalgia of missing out on something, to appreciating workers who are looked down on as the scum of the earth; eve sometimes dabbling in Buddhist religiosity.

I have noticed that some of his music appear as if the instruments are slightly out of tune, but to an effect that is pleasant to the ear, the most notable being Michi Teyu Ku(Overflowing); but I can't exactly place my finger on what causes it to sound this way. My best theory is that western key placements on instruments have been standardized, and in some parts of the world, they still rely on their distinct notes. I came to this deduction based on the fact that even western key placements in the past used to sound vastly different on different instruments, even of the same type, such that they would skip entire semitones/full tone pitches from what is nowadays conventional. I guess that is the strange allure that people find in his music.

So: What is your take on this?