Roboto does not support Japanese Kanji. However, if you are building a bilingual site (English + Japanese), you might try to pair Hiragino (JP) with Roboto (Latin). But since you can't host Hiragino, you can use Noto Sans JP for Japanese and Roboto for English. The stylistic overlap is excellent.
The reality, however, is disappointing. You will not find Hiragino Kaku Gothic Pro on Google Fonts. This article explains why this iconic font is absent from the platform, its actual role in modern web design, and—most importantly—the best Google Font alternatives to achieve a similar aesthetic. hiragino kaku gothic pro google font
: A versatile set that offers various weights similar to the Hiragino family. Google Fonts 2. Using Hiragino in Web CSS Roboto does not support Japanese Kanji