Where does “ひとみ” come from?

ひとみ (Japanese) comes from Japanese 人, from Proto-Japonic *pitə — one.

Ancestry of “ひとみ”, step by step

ひとみ traces back through two separate lines of ancestry.

via Japanese

StepLanguageWordMeaning
1Japanesea person, human; an individual; mankind, people
2Proto-Japonic*pitəone

via Japanese

StepLanguageWordMeaning
1Japaneseseeing, looking; the look or appearance of...
2Middle Chinese
Every word from Proto-Japonic *pitəEvery word from Japanese