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There is a main Dark Path which starts around Day 69 if all characters are kept up to date.
Sarah and Sophia have individual Dark Path variations. Good Path story branches are those alternative choices Not Marked as Dark.
MC still has plenty of fun fetishes on the Good Path, just does not slowly become more sadistic or vengeful toward others, like he does on Dark Path. Group sex is mostly Dark Path, Lesbian and Sleep sex still happen on both paths.
Individual character storylines do change on Dark Path, with some characters relocating and their loved ones wondering where they went.
Completionists will want to have 2 or 3 path saves, but if you're more into BDSM, Sharing, NTR, Training and Corruption, Dark Path is your game. If you're looking for harem, love, pregnancy, and still having wild sex but with women professing appreciation, Good Path is your game.
There are Neutral Characters who exist and do not have split stories, so they're present regardless of path choice.