Yuna Hiiragi, supported by her older sister Ayaka Hiiragi, has continued to protect the Yugahara Ryokan, a hot spring inn with over a hundred years of history.

The town where the inn is located is peaceful, though not exciting, and Yuna enjoys her student life with her childhood friend Haruka Kasuga and the transfer student, Shiyo Kinosato.

However, at the start of summer vacation, a shocking event occurs. It is discovered that the inn's manager had borrowed a large sum of money using the inn's title deed as collateral. The manager disappears, and in his place come suspicious men and a mysterious beauty, Mari Fujimoto. The title deed had been transferred to them without the sisters' knowledge.

As the Hiiragi sisters try to regain the inn, the men make a proposal: if they follow their instructions and continue managing the inn, they won't be fired. With no other choice, they accept the conditions, and for a while, things seem to calm down. But one day, Ayaka, her older sister, collapses from mysterious overwork. Yuna eventually learns the cause of her sister's overwork, discovering that their words were a sweet trap…