Ibara Hime

Ririko and Suzuki were sister and brother separated by one year.
Like twins in their understanding and love, the grew up the best of friends.
Time changed them, however, and while they still attended school
as classmates, and shared the same home, they rarely spent time together.

Rikiko now had her first boyfriend.
She hoped to repair her delicate relationship with Suzuki, but...

Incest / school / melancholy game.
There is not a happy ending for the protagonist.
There is forbidden love between siblings.

Explore the routes of Thorn Princess if your heart can bear it.
Unwilling affairs. Bloodshed. Depression. Sickness. Death. No salvation.
These are the themes. Please be warned.

[From DLSite English]