So im not an expert, but I believe i have seen someone ask this sort of thing before in a different game (dont remember the game's name)
Anyways, if memory serves, it comes down to mostly two reasons they do this sort of thing.
1. To give the player an option in kinks/fantasy. The story in this game wouldnt work well if Leslie was given the option of being your land lady, tutor, maid, or whatever.
2. Country the game is made in. Certain countries prohibit incest in games. If the game is being developed in one of these countries, the devolpers give you the option to change the title/ relationship to the MC as a work around for players. Im guessing breadman is not in one of these countries.
So the story, unless im mistaken of course, is safe.