Overview
"夜這い" (yobai) is a traditional Japanese practice where a man sneaks into the bedroom of a woman, typically his betrothed or wife, during the night for sexual intimacy. It has historical and cultural significance in Japan, often associated with courtship and marriage customs in rural areas.
It is often misunderstood, but originally, a night crawling was something that was done with the consent of both parties, and if the woman did not like it, she could refuse (although, depending on the time and circumstances, it is thought that there were also violent acts that were almost like rape).
Traditionally, men are the ones who're doing the night crawling, but many artworks in Pixiv depict women as being the ones who do the night crawling.