Now updated to include volumes five and six.
Soft-faced shoujo character design style is typically at odds with nudity, but not this time.
Seems like kind of a somber little story. Sex isn’t always happy sex, in fact unhappiness seems to be a prevalent theme in this one. Hard not to appreciate the combination of quality character design and nudity though.
Himegoto Juukyuusai no Seifuku (6 volumes, ongoing)