It took several bottles of Itoen tea to complete the set, but I got the last one today. After a half-dozen doubles (I really need to wear my glasses when shopping for these), I have all 9.
The attention-seeking trio wearing the antlers and cat ears are (left to right)
琴吹 紬 Kotobuki Tsumugi, 中野 梓 Nakano Azusa & 平沢 唯 Hirasawa Yui.
The bright nerdy trio wearing Santa hats are (l-r)
田井中 律 Tainaka Ritsu, 山中 さわ子 Yamanaka Sawako & 真鍋 和 Manabe Nodoka.
The final trio of precocious cuties are (l-r)
平沢 憂 Hirasawa Ui, 鈴木 純 Suzuki Jun & 秋山 澪 Akiyama Mio.
I may have their descriptions slightly off base, but I'm sure I'll hear about it from their fans.
All I know is that they'll be adorning my tree.