Before you read this Manga, go read the main series. Kagefumi Merry is a side story that has nothing to do with the main plot of the main series but it also doesn't explain nothing about what is happening. To understand this Manga fully read the main series Yumekui Merry.
Story(5/10): Nothing special, its a meh sub-plot that has nothing to do with the main plot, and only 3 chapters long so don't expect much. Cool for those who are a fan of Yumekui Merry but if you never read Yumekui Merry than this manga's story is gonna be even worse for you.
Art(4/10): Compared to Yumekui
Merry the art in this isn't that good, and the first chapter suffers from what looks to be drafts instead of the final product. Overall the art is disappointing.
Characters(5/10): All new characters and villains but you don't really start to care or feel for these characters because of how short it is. Not only that but they get out shined by the main cast in the main series.
Enjoyment(6/10): It was a cool short read I guess, its fine in my opinion but with the sloppy art and very short story its not all what it could've been.
Final Verdict(5/10): Its a meh read for those who are a fan of Yumekui Merry so don't read this unless you read the main series first which has better art and characters, the main problem is how the main series just out performs this short read in every way.