Kaori and Jessie J
Notice their heads (jaws, chins, ears) though Jessie J has a wider jaw/overall.
As I've watched videos about the voice, I have come to see how the shape and dimensions of a person's face/head (the resonance spaces) determine the vocal tone and voice type - in conjunction with the vocal cord length/size. A video I watched spoke about how singers with larger jawlines/heads tended to have bigger voices - e.g. powerhouse singers of different traditions like Jennifer Hudson, Jessie J, Joan Sutherland, Birgit Nilsson - due in part to their the natural endowments. Add to that lung capacity and lots of training to maximize breath, move resonance, and use vibrato and you have a standout voice.
In FJ, Kaori's more pronounced jaw, the larger forehead, jaw, (basically larger head size compared with Keiko and others) gives her a lot more naturally reverberant space for her voice, The position of her eyes, nose, etc., and how she moves her air when singing helps shape the tone.
Kaori has a bigger voice and is able to belt powerfully using less effort than a, say, Wakana, or Hikaru, or even Joelle. She probably has a larger lung capacity as well with her larger frame.
The great thing about developing singing technique is that, even with smaller facial features and voice (smaller natural resonance) you can use advanced techniques to still project your voice powerfully using other ways of resonating -
e.g. Yuriko's masterful use of the mask and her unique vibrato to take space and stand out often without opening her mouth so wide - without resorting to yelling for power / loudness or overdoing the use of nasality.
Maybe this post should be in the
https://forum.canta-per-me.net/thre...olo-work-hikaru-kaori-keiko-wakana-etc.12655/ thread. I don't know.