well a lot of linguists consider Japanese to be an Altaic language.
In 1909, Shinkichi Hashimoto found that Old Japanese had two groups of the vowels /i/, /e/, and /o/, so there were 8 vowels and everyone could distinguish them clearly, except those from the distant Aduma people in the East. Further studies on the usage and distinction of these vowels indicate that Old Japanese had vowel accordance, something close to vowel harmony, which is characteristic of Altaic languages like Turkish, Mongolian, and Tungusic languages. It's one of important aspects that indicates the relation of Altaic languages and Japanese, but this vowel accordance and even the distinction of two groups of vowels disappeared by the 10th century. Isn't this a linguistic version of same phenomena, that the average Japanese became 160 cm tall hundreds of years after the shock wave from Korea? As time passes, the Japanese language has been losing the characteristic Altaic part of its origin.
Origin of the Japanese People and Language
if you look at the structure of the Japanese words, its harmonical like Mongolian Hungarian Turkish.
for example
Mitsubishi
Yokohama
kawasaki
you see how the vowels are in harmonical order? ka-wa-sa-ki
and Turkish for example,
kanayan
derece
buyucu
same concept in Turkish