The ThemedHarem's theme: LittleSisterHeroine.
Rolling Updates, Needs a Better Description A sort-of sub-genre of hentai and ecchi harem stories, in which the main characteristic is that the girls in the Love Dodecahedron (or a Love Dodecaehdron-sized subset of the main Love Dodecahedron) are all sisters, most typically of the blood-related variety and sharing at least one parent between them all. The protagonist himself, however, is rarely related to the sisters. This can also often lead to situations where several of the sisters get it on with the guy at the same time. This trope is the result of taking the premise of Sibling Triangle up to eleven and blowing it to Love Dodecahedron proportions. Do also note that while it's usually "several sisters, one guy", cases of "several brothers, one guy" do exist, but are rarer than former variant due to Double Standard.
Examples:Anime & Manga