Not Japanese Music, but I really like this K-pop song because the singer's voice is kind of cute sounding.
Not cute but might be to your liking Mili - Yubikiri-Genman Wataru Sena ft Sana - Hitoritabi Sana - Goodbye, Ms Floral Thief Minami - Monologue Yorushika - Say it Yorushika - Hitchcock https://youtu.be/t7MBzMP4OzY
i think the closest ones i have on my list Spoiler: would be... granted, i don't really feel like they're quite what you're lookin' for. i had a few others, but eventually phased 'em out after sitting 'em on for so long. mainly because of either heavy autotuner or mixed vocals.