Poolside. A faint scent of chlorine, with a deep, deep nose.
The casual youth and casual days suddenly change the figure.
"That day, that morning, my body changed to something completely different."

Kei Suemori, a first-year high school swimmer, almost drowns in a swimming pool. His classmate Shizuku Kawano dives in to save his life, kissing him underwater to give him air, and afterwards his body changes to the one of a kappa. Trying to learn how to become human again, he bonds with Shizuku who is a kappa as well. As the distance between the two becomes closer, a new kappa appears in front of them, and things take a turn for the worse. A heart-wrenching, cross-species love story!