>>281553269
Hidamari Sketch Anthology Comic vol 1, chapter 6.

They're a bunch of "official" "doujins" by other authors. Meaning you can buy the volumes like real manga volumes from stores, but they're not by Ume herself. And the authors aren't necessarily doing it just because they're fans.

Some of them are well known, like I guess Yuru Camp and Yuyushiki authors might be for wide fans.

https://dynasty-scans.com/series/hidamari_sketch_anthology_comic
https://dynasty-scans.com/series/hidamari_sketch_story_anthology_comic