From PROzess:

Okada Keiichi nearly drowned in his childhood, which left him with a trauma for water. Now he faints on the slightest touch with water. To his grief, his girlfriend takes him to the pool to charm him with her swimsuit. By accident Keiichi falls into the pool and gets rescued by the swimming instructor, Mizushima. Keiichi senses something special about her and even Mizushima seems to knows something about Keiichi's past. What will happen to Keiichi now?