https://www.youtube.com/watch?v=qTf5aRThczICan more musically learned anons help me understand what about her voice makes me like it?
I feel like her tone and enunciation are very clear, and her waver on longer/held notes is just gentle enough to be impactful without being distracting. But, I don't really have any more than a laypersons understanding of music theory and vocal performance, so if anon can see aspects of Sumeragi's performance that are unique that I can't identify, I'd find that interesting.
Her eng is also really natural sounding, if this song is to be trusted:
https://www.youtube.com/watch?v=9NhYtyeigwg 