Half a year ago, Hiro was welcomed into the family as the younger stepbrother. Recently, his body has been growing rapidly and he’s started to look more grown-up. Since he’s their very first little brother, everyone treats him with zero distance, doting on him completely. The adolescent Hiro gets sexual aroused and… ends up having his first ejaculation right in front of the whole family…? Because he only became their stepbrother half a year ago, the sense of “being family” hasn’t really taken hold yet. When they catch sight of Hiro’s huge thing, everyone in the family can’t help but see him in that way…? Is a lewd life with this big-breasted family about to begin?