Kuonji Kiri

The protagonist's younger sister.
She is the head of the class committee and a very diligent girl.
As she enters puberty, she begins to be aware of her brother as a man. But thanks to Riri, who possesses her, she ends up having sex with her brother, skipping the whole bonding process.
Her situation is becoming increasingly unstable, as her body now contains two souls, her own and Riri's.
What fate awaits her...?