Ordinary student Sousuke has long admired the Nanase sisters, Arisa and Mika, from afar as the school’s glamorous idols. His quiet routine shifts when Mika approaches him after classes, leading to an unexpected reunion where the three learn their parents have married following a chance meeting abroad. Now preparing to share a home as stepsiblings, Sousuke adjusts to the sudden closeness and the delicate new boundaries of their daily lives.