Good explanation, however slightly more correctly the Japanese "r" varies between a postalveolar flap [ɽ] and an alveolar lateral flap [ɺ]. Okada, Hideo (1991). Japanese". Journal of the International Phonetic Association 21 (2): 94–96.Note that isn't the correct symbol for a postalveolar flap (there isn't one). In Japanese "l" and "r" sounds are allophones.