The 'r' in Japanese is a "tap-flap" and is best approximated in English with 'r' because it's too hard to explain that the closest approximation to it is some dialects of English's "tt" sound, such as in "letter" where the "t" sound isn't really pronounced at all, but instead basically becomes a lazy version of the sound.
The 'r' in Japanese is a
The 'r' in Japanese is a "tap-flap" and is best approximated in English with 'r' because it's too hard to explain that the closest approximation to it is some dialects of English's "tt" sound, such as in "letter" where the "t" sound isn't really pronounced at all, but instead basically becomes a lazy version of the sound.