S1 No.1 Style presents an aggressive girl and sister-themed NTR training story. Aoi Tsukasa, my brother's ex-girlfriend, suddenly appears. I learn she was sexually trained and used by my brother until he made her sink into debt and abandoned her. Feeling responsible, I agree to take on her debt, but with no way to repay it, I follow my brother's instructions to bring her to a hotel. There, I'm stripped naked and subjected to the same intense sexual training my brother inflicted on her. Though I resist at first, her relentless and shamelessly arousing techniques gradually take hold of my body. Before long, I find myself unable to get aroused by anyone except Aoi Tsukasa.