The morning after his high school graduation ceremony, Araragi goes to the bathroom to wash his face but is struck by the sensation that his reflection is watching him. Touching the mirror, Araragii’s hand passes straight through and he is sucked into a mysterious world.

Schoolchildren Norimichi, Yuusuke, and Junichi want to know if fireworks look round or flat from the side. They make a plan to find the answer at a fireworks display, while Nazuna schemes to run away with Norimichi or Yuusuke, whoever wins at the pool.