Pictures that group together at least three of the Old Maids: a group of Touhou characters who possess an aura of maturity, possibility from being many centuries old.
Current members include Hijiri Byakuren, Saigyouji Yuyuko, Yagokoro Eirin, Yasaka Kanako, and Yakumo Yukari. Kazami Yuuka was once occasionally featured with this group, but her appearences have decreased with the addition of Byakuren to the group. Shinki and Mima are sometimes, but rarely, included with this group also. Yuuka, Shinki, and Mima, having all originated in the PC-98 games, are sometimes referred to as the "Original Old Maids Alliance".
(as said from danbooru wiki)