GiveUpTheGhost said:
Are Ryuunu and Kobayashi Yuuji the same artists, of the same circle, or separate entirely? Uploads from the Pixiv account associated with the former are tagged with the latter.
Circle "Sage" consists of two main members (Cha-Peru and [[Ryunnu]]).
Kobayashi Yuuji was just a guest artist of that doujin.
See also Daijin's comment. (comment #1054879)