In S03E10, why does Kaguya address Moeha (Chika Fujiwara's imouto) by 1st name only after previously, in S02E02,
A - expressing reluctance to do the same for Kei (Miyuki Shirogane's imouto) and
B - addressing Moeha as Moeha-san?
Actually, afaiu, 'Moeha-san' is too polite, but I figured it was just Kaguya's thing or Kaguya's school's thing (Quote: 'In that school, everybody pretty much uses keigo with everybody else').
This is the 1st time I've ever called someone by their 1st name only. - Kaguya about calling Kei Shirogane by 1st name.
Note 1: Kaguya even wanted to address Kei as Shirogane-san, then Kei-san and then Kei-chan.
Note 2: Sort of cross-posted in Japanese SE: Changing the way you address someone without your relationship having changed