Takumi's life is turned upside down when his father brings home two sisters, the cold Saori and the gentle Yui, to live with them. While Takumi struggles to bridge the gap with the distant Saori, he is blindsided by a passionate Christmas Eve confession from his close companion, Mii-nee, who fears losing him to the newcomers. Following an intimate encounter with Mii-nee, Takumi finds himself torn between his deep bond with her and his growing attraction to Saori.