蠱蝶の夢　「もう、やめて……！これ以上私の精神を穢さないで……！」（Kochou no Yume "Mou, Yamete...! Kore Ijou Watashi no Kokoro o Kegasanaide...!"）

Our protagonist, Katsuragi Haruto, lives with his beautiful older sister, Katsuragi Chitose, who dotes on her younger brother.
Since they lost their parents in a tragic accident several years ago, the two have been living together in the house their parents left them. However, the siblings eventually became dependent on each other, and eventually they crossed the line. Night after night, the siblings whisper sweet words of love to each other and develop a relationship where their bodies lustfully intertwine. They deeply shared everything, happy and sad, and even the pleasures of each night.

But once again, a cruel fate tore the loving brother and sister apart.
Chitose was tragically involved in a traffic accident.
Fortunately, there were few external injuries, but Chitose...the sister still lied in a hospital bed in a unknown state.
For several months since then, Haruto has been visiting Chitose and caring for her diligently.
One day, Haruto fell asleep in the hospital room and he had a mysterious dream and waked up to find that...

"Hehehehe. Do you miss your sister that much?"

Suddenly, a dazzling light appears before Haruto's eyes, and a mysterious girl appears.
The girl introduces herself as "Eru," reveals that she is not human, and promises to help Haruto. Then, she whispers a proposal to him:

"To save Chitose, have sex as much as you can and collect the essence of other women. I'll lend you my power."

This was the proposal from her, who still retains the appearance of an innocent young girl.
Haruto doesn't know if Elle is an "angel" or a "devil." But clinging to this glimmer of hope, he decides to carry out the "essence collection" she suggested.

...The seasons change, and the cherry blossoms begin to bloom. With beautiful girls as the target, the curtain rises on a lust-filled erotic drama.