Shinji planned a hot springs trip alone with his wife, but due to sudden circumstances, his sister-in-law Ena joins them. Slightly annoyed, Shinji finds himself alone with Ena when his wife rushes off for work. Ena opens up about a personal struggle, giving Shinji the chance to grow closer to her. Gradually moved by Ena's warmth and affection, their relationship takes a step further. Sexually starved for a long time, Shinji tells himself it's "just once," but when Ena slips under his futon, one time isn't enough. Caught off guard by the turn of events, Shinji begins to realize the shifting emotions within him.