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序章 被留下的人
Prologue: The One Who Stayed
The dismissal bell cut the corridor in two.
The first half was running footsteps and the rasp of zippers yanked open. The second half held only a mop, a bucket, and a name circled in red on the duty roster.
Aoba Tōru looked at his own name and sighed. Still stuck wiping the blackboard in his third year—it sounded miserable. In truth, he had volunteered to take someone else’s shift. That person had cram school. He did not.
The air in the classroom cooled by degrees. Outside the window the cherry trees were past their season; only a few blossoms refused to finish falling. Tōru wiped the board clean, set the chairs up on the desks, and was about to close the window when he heard, from the empty classroom next door, a faint sound like a fingernail scraping chalk.
He ought to leave it. Duty did not include minding other people’s business.
But the sound was too regular, as if someone were writing, stroke by stroke, a problem that would never be finished.