Izumi Momoka is a quiet, diligent honor student. She never skips classes and only watches swimming lessons. But as her homeroom teacher, she can't actually swim, so he offers to give her one-on-one after-school lessons. Momoka improves rapidly, and his eyes are filled with joy. However, the school swimsuit suits this pale, slender girl far too well. Wet with water, it clings tightly to her body. The navy blue swimsuit accentuates the paleness of her skin. And above all else... her unconsciously erect nipples. Her pointy nipples are visible even through the swimsuit. He knows it's wrong as her homeroom teacher, but he still wants to touch them. He wants to touch them even if it means wasting his life. A nipple unconsciously protruding from a school swimsuit can drive a man crazy. Faced with an innocent girl still growing, the middle-aged teacher decides to abandon his reason.