A young man visits Hinawari Onsen, where the story takes place, and is stunned when he sees that the innkeeper and her waitress both have incredible breasts. This is the story of an erotic romance in a mysterious, hidden hot spring. Keitaro Yamagishi, the main character, visits a hot spring resort after a long day at work. He finds out that the beautiful married landlady there is having a secret affair with a mysterious young beauty, A youthful sense of justice and morality lead him to want to find out more. The married woman who allowed her skin to be touched by the same sex... and the mysterious young woman, who has a secret. And finally, the young waitress in the middle of all this. When she finds out about it, she, amazingly, joins in. Their relationship become deeply and intricately entangled, and the story takes an unexpected turn...