Outgrowing only girls, Overtake boys, Growth sound. Handrail Arc

Each time that mysterious sound echoes from the classroom, dormant energy awakens within her body.
The staircase handrail at school was once something the protagonist could casually rest his elbow on. But as she develops day by day and rapidly grows taller, it becomes a cruel yardstick that vividly displays the changes taking place during her extraordinary growth.
The overwhelming sense of realism as the girl, once so small, gradually catches up to and surpasses the protagonist's height over the course of three days, then six days, and beyond. The gaze of the girl he once looked down upon slowly rises to meet his own, before eventually looking down at him from far above. The exhilaration and despair of that reversal unfold in vivid detail.