>>12728038Their voice ranges are similar and would work splendidly together. The main difference I see is that Suisei has more natural power behind her voice than Okayu. It sounds like Suisei had some vocal training or at least some guidance from professionals in the past, and Okayu said she never really had real voice training. Then again with Okayu it's hard to tell these days how much power she really has in her voice because in every karaoke stream now she chooses to sing in her high cutesy voice instead of her natural voice, so she's not using her full potential. Her karaoke of "King" from the beginning of the year gives us some insight to her full power, as do Okayu's karaokes from much earlier on in her career.
https://www.youtube.com/watch?v=7UiIcIdmeRY 