Gradation of Happiness
Gradation of Happiness is a series of graphic artwork showcased on a newer (but still defunct) version of the OSD website. It's unknown whether every work in the series is showcased here; this may not be the case, seeing that some of the other sections (Anonymous Animals) are known to be incomplete.
This page is the only known reference to the series, and source of the artwork.
Sato can be seen editing one of these images at approximately 2:35 in the Next Beat interview.