Also known as: 肛交之后, ぽっかりアナル
The aftermath of Anal penetration, be it from from a Penis or a Dildo. See After Sex for guidelines on what to look for.
Try not to confuse this with Imminent Anal, which may look similar to this in small thumbnails.
This and Anal contextually shouldn't occur at the same time, but it's possible in a Comic where anal sex is occurring in one panel, then the next panel has the aftermath.