Also known as: 阴道的, 阴道性行为, 膣の, 阴道插入
Vaginal penetration by any means, whether by Sex, Fingering, sex toys, Tentacles, etc.
If, and only if, a Penis is doing the penetrating, the image should also be tagged Sex.
Do not confuse this tag with the Pussy (vagina) tag, which refers to female genitalia. If the character's vagina is clearly seen, it should be tagged with Pussy.