It was a perfectly ordinary Monday.
Which is why it felt strange.
Haru sat by the window, watching cherry blossoms drift past like slow snow. The teacher's voice blurred into background noise—just another day, just another lesson he wouldn't remember.
"Today, we have a transfer student."
That alone was unusual.
But what came next wasn't.
"Please come in."
The door slid open.
And that's when Haru felt it.
A pause.
Like the world skipped a beat.
She stepped in quietly—long black hair, soft eyes, and a smile that didn't quite belong to this world.
"Tachibana Yuki," she said gently. "Nice to meet you."
Haru blinked.
No one reacted.
No whispers. No curiosity. Nothing.
It was like… she had always been there.
Except—
She hadn't.
After school, Haru found her sitting alone on the rooftop.
"You noticed, didn't you?" she asked without turning around.
"…Noticed what?"
She smiled.
"That no one remembers when I'm gone."
The wind brushed past them, carrying petals into the sky.
"I don't exist every day," she continued. "Only on the days you won't use."
Haru frowned. "That doesn't make any sense."
"I know."
She turned to him, her eyes unusually bright.
"But… will you spend today with me anyway?"