Reimu looks very much like a child, so it's a little disturbing. On the other hand, if this is during The Young Girl and the Little Girl Of Hakurei, then it might make more sense where Yukari's being protective rather than sexual, and Reimu is mentally an adult.
This was drawn a couple weeks after "The Young Girl..." was published, so it's probably fair to assume it's a similar continuity.
PerCol always had a very different take on the Reimu/Yukari dynamic as I recall, certainly made some pretty killer art of the two.