The emoticon that shows the lips being tugged forward on the backwards pull whilst sucking on something, as seen from an overhead or semi-overhead viewpoint. Typically this means fellatio, but it can also be seen when a character is sucking on a more innocuous object, such as a popsicle or pen.
The equivalent pixiv tags are ひょっとこフェラ (Hyottoko fellatio) or バキュームフェラ (Vacuum fellatio).
The following tags are aliased to this tag: blowjob_face and vacuum_fellatio (learn more).