The season is winter. It was around the time when February was just about to begin. The protagonist, Misato Juri, finds an out-of-season butterfly in the garden of his apartment.

It is a strange, indescribably beautiful butterfly that gleams a lustrous lapis blue. But its brilliant wings are cruelly shriveled, leaving it unable to fly; clinging desperately to the withered branch.

Juri decided to name the deformed butterfly, which was just waiting for the moment of its death, "Ao" and to protect it warmly.

――The next day. When I got home, an unfamiliar girl was collapsed inside the room.

At first glance she looks about the same age as Juri— wearing a dress with lapis-blue patterned wings that seem oddly familiar, and surrounded for some reason by shards of an insect cage...

"My name is Ao. I fell in love with you at first sight."

When she woke up, she introduced herself with a familiar name and conveyed her straightforward love to Juri.

And she had a mysterious ability.

An infallible power of predicting the future— And as a thank-you for saving her, she reads Juris fortune and gives a shocking answer.

"……Im sorry to say this, but..." ――"It seems that you will die in nine days."

The butterfly Juri protected turned into a human girl— and suddenly delivered a death sentence.