Hiragino Sans W9 _top_ Link
Why use W9 instead of just applying a faux-bold (synthetic bolding) to W6? Because synthetic bolding destroys calligraphic quality. True Hiragino Sans W9 possesses specific design traits:
(formerly Dainippon Screen Mfg.), it is a staple of high-impact visual design in Japan and is widely recognized for its inclusion in Apple's macOS and iOS operating systems. Overview of Hiragino Sans W9 Weight & Impact hiragino sans w9