Manga 61369 Imasugu Oniichan Ni Imouto Da Tte Iitai

Their are basically two mangas here crammed into one.

One manga is a heart-warming story about a boy who is still mourning his dead mother, as he comes to accept his new step-mother and step-sister/brother. That story is great: great characters and character development, good resolution. The forbidden-romance part of this plot is its weakest link, but it still works well enough.

The other story is a school harem manga. Actually, to call it a story is giving it too much credit, because it doesn't make any sense. Girls join the harem with no warning or explanation--suddenly, they are just there. None ... of them have explained back-stories, none of them get any kind of resolution, and they are drawn almost identically so you can't really tell who is who (not that it matters).

It feels like someone wrote a solid, dramatic, step-sibling romance manga and inserted randomly selected chapters from a bad harem manga throughout. And it works about that well.