"Ane Jiyoku Tsukushi: Nee-san no Shitagi" follows ordinary student Mizuki, whose perfect older sisters—Ema, the poised student council president, and Ruka, the idol-like beauty—tease and rely on him at home despite their flawless public images. Everything shifts when the sisters discover Mizuki has a girlfriend, sparking jealousy that ignites taboo seduction and intimate encounters, blending emotional tension with intense eroticism. As boundaries blur, the siblings navigate forbidden desires, leading to passionate, provocative moments that redefine their family dynamic.