The voiced retroflex approximant is a type of consonant used in some languages. The symbol in the International Phonetic Alphabet that represents this sound is ⟨ɻ⟩, and the equivalent X-SAMPA symbol is r\`. The IPA symbol is a turned lowercase letter r with a rightward hook protruding from the lower right of the letter.
Apical. As an initial in free variation between fricative and approximant, but never has friction as strong as a true fricative (Chinese "fully muddy"/全浊-class) to trigger a (free or conditional) devoicing or postvoicing into /ʐ̥ʱ/, nor weak enough to become an apical vowel. As a rime it's an apical vowel that is frequently coarticulated with a close near-back unrounded vowel /ɨ̟/ (thus phonetically [ɻ̺͢ɨ̟͡ɻ̺̞̍˥˩ku̯ɑ͢ŋ˥], but this phonetic representation should be avoided as the tie-bar for coarticulation may be misunderstood as a sliding into an erhuarhotic vowel, a phonemically distinct syllable in Chinese), but it can be prolonged indefinitely and never truly developed into an /ɨ̟/. Both the consonant and the vowel may gain some friction especially when prolonged to force a more "distinct/clear" effect in teaching or when swearing, and thus it may be inaccurately transcribed as fricative [ʐ] both as initial and as rime (when precision is necessary, a true fricative in Wu Chinese may be transcribed as [ʐ̥ʱ], as that's how it's pronounced in the first syllable). See Standard Chinese phonology.
The character 日 (sun), when pronounced with an overall strengthened friction (on both z and ɿ), may likely be understood as a profanity, thus pronouncing as an approximant is important; but the two do not form a minimal pair, because the profanity can also be pronounced with little friction (though in some other dialects they further evolved to form a minimal pair).