The title is all wrong: Literally it's "The S in do-S is for...", but I can't think of a good way to render than in English so I don't really have a suggestion for what to use instead.

(Also, the implied full title is "The S in do-S is for Suteki", which is the punchline of the last page.)

It's for S-tier.

Since the uploads of the colored version of this wonderful work have bit the dust, here are the colored versions on better hosting.
Page 1 , page 2 , page 3 , page 4 , page 5 , page 6 , page 7 , page 8 , page 9