I finally found it. It's from Kaiten Sommelier, it's called "Private Risshin Academy." It's also called Kaiten 19. I removed the Azumanga Daioh and Yomi tags, since neither are correct.
comment #18347 Her name is Honami Totsuka, and the only thing she has in common with Yomi is that they both wear glasses and have long hair. Download the link I provided already and you'll see for yourself.
I looked at the manga... it turns out this has been modified to say "Yomi-chan" instead of "Honami-chan". You can see it in the third panel. ...maybe I better just translate this instead.
Ah, thanks for the tags. I can read a bit of Japanese, and the "Yomi-chan" confused me, too. I gues someone just really wanted to see Yomi deepthroat. I can't say I blame him, Yomi's the hottest of the AzuDai girls. But they didn't have to modify this scan to see that. Just check out the Kaiten 14 doujin that's included in the link above to see her taking cocks all the way to the root in both the mouth and ass.
So it's just someone that looks like Yomi and is called "Yomi-chan"?
Ah- the tip's touching... is it really okay to push it in?Yup~And then, finally, the penis slides slowly and deeply into my throat, all the way to the base...When I swallow, the penis flinches so happily~W-well, if you say so...