instant loss
即堕ち2コマシリーズ 即堕ち2コマ 即落ち2コマシリーズ 即堕ち
Images themed on the "almost comically instant loss" situations. Often used with mating press and chinpo ni wa katenakatta yo. Though not all instant loss post involves sexual engagements.
This tag does not necessarily have to follow the 2koma format, and can apply to two separately uploaded posts, so long as they depict a series of sequential events.
Pixiv Encyclopedia said that it started as a personal webcomic series by a certain artist. After that, however, the original webcomics were deleted for some reason. The series name is now used as a general tag on pixiv.
Note: Just because a post depicts an SFW scene followed by an NSFW scene, it doesn't necessarily mean it's an "instant loss" situation.