山奥にある秘湯と名高い家族経営の温泉旅館。だが、両親が不慮の事故で亡くなった。4姉妹は両親の形見でもある旅館を継ぐことを決意する。 しかし、彼女たちに旅館を営む能力もあるわけはなく、潰れる手前まで追い込まれた。だが、彼女たちは自慢の巨乳を駆使し、見事旅館の立て直すプロジェクトSEX物語。A family-run hot spring inn deep in the mountains is famous for its secluded hot springs. When the parents die in a freak accident、 the four sisters decide to take over the inn、 which is also their parents' legacy. However、 there is no way that they are capable of running the inn、 and they are driven to the brink of collapse. However、 the sisters make use of their big breasts and successfully rebuild the inn. Project: SEX tales.
