I am going to base mine off the popularity among the Japanese public's rankings via things like Ranker and the most searched idols.
- 1st Gen: Shoo from S.E.S (the only Japanese female K-Pop idol of gen 1)
- 2nd Generation: Lee Ahyumi from Sugar (She would go on to have a very successful solo career in Japan as both a singer and actress, after leaving SM Entertainment in 2006).
- 3rd gen: Sana, she is currently number one amongst all Japanese K-Pop idols regardless of generation according to the Japanese rankings. Momo and Mina follow her in the ranking immediately after her in 2 and 3 respectively.
- 4th gen: Sakura is currently #4 in rankings of most beloved Japanese K-Pop idols of all time, Giselle just barely made the top 10 of the list. Kazuha is the next highest 4th gen Japanese K-Pop idol after her in the listing. Then it's Rei from IVE. Followed by Tsuki from Billlie.
- 5th gen: ASA is currently #8 on the list of Japanese K-Pop idols who are most beloved. Moka is all the way down at #13 in the listing. Please do not shoot the messenger Ill-It fans.
Sugar is considered first generation.