Nu'er Guo Chuanqi

In the Woman Country, the respectful Nan Bei has decreed that only men of aristocratic backgrounds are to be allowed to marry and those of low status are to be sold as slaves to fulfill the whims of women. ShenNan is an ordinary modern day middle school student, but the fact is she's anything but, as a haunted incident at school allows her to pass through to the Woman Country where she experiences the monarch life of few illustrious old gentlemen.

(Source: M Scanlations)