That was quite short but cute. I'd really like to see how their relationship had developed into them being so openly affectionate with each other, though.
Oh heck, check out this artist's pixiv. It's full of the cutest fluffiest Aya x Reimu! There are dozens more little comics, and lots of nice single images. (warning though: some R-18 with futa. Avoid/Dig In, depending on your tastes)