Gimai Seikatsu

Story:

Under one roof, from peers to brother and sister. Asamura Yuuta winds up with a new stepsister, Ayase Saki, who just so happens to be the most beautiful student of the year, following his father's second marriage. Their parents' prior marriages have taught them valuable lessons about man-woman interactions, so they make a pledge to one another to just maintain a vague and comfortable distance rather than to get too near or too far apart. While Yuta is unclear of how to treat Saki correctly, Saki, having worked alone for her family's sake, doesn't know how to properly rely on others. Perched atop somewhat level terrain, these two gradually come to understand what it's like to live together comfortably.