“My sister… Is she really my sister?” Can you truly say, without a shred of doubt, that the person you love by your side is family?

Haruka lost her parents when she was just a child. For a time she was separated from her older sister, Yurina, but now the two live together again, seemingly close as ever. To Haruka, beautiful Yurina is the very picture of the perfect sister.

But even so, two unsettling doubts have taken root in her heart. The first one is that every time Yurina starts dating someone new, she always calls him her “first love.”. And the second one is whether Yurina is truly her sister at all.

Desperate to shake off these suspicions, Haruka opens her sister’s old graduation album. What she discovers inside leaves her reeling.

And one night, her worst fears take shape before her eyes. Haruka catches Yurina “carving up” her so-called first love with a kitchen knife…?!