I think I know what is going on.
Kita is a clone of Minami's mum. They underwent the same medical procedures because they had the same disease. Also, it is possible that the scar (which is not shown) could be a c section? That is not very likely, but it is possible given the technical advances in this manga.
Would this fall under incest? Probably, but I do not mi d one bit. I am looking forward to the next chapter.