The main character, Haruhisa, is living a peaceful but happy life with his first girlfriend, Miku.
One day, the protagonist is called to Miku’s house and meets her older sister, Ruri.
Ruri actively wants to have skinship with Haruhisa and even does naughty things with him.
She is the main character who finally crosses the line with Ruri.
However, it doesn’t end there, and the sex with her Ruri escalates more and more,
The main character gets stuck in the swamp…