@ DiaStarkLordoftheBed ask 10 people and all will say something different, but you could start with the VN (if available) or "normal" stay/night or you can start with zero.
@ DiaStarkLordoftheBed If you're looking to watch the fate anime rather than read the vn I highly recommend starting with Fate Zero by studio Ufotable as it is widely considered the best fate adaptation to date and there's an extremely impactful plot point at its conclusion which will be completely spoiled if you watch any other. Its technically a prequel so by watching it you have some "spoilers" towards later fate series, however it spoils significantly less and is also far more worthwhile to watch unspoiled in my personal opinion. You might wish to learn a bit of of basic spoiler free fate lore (basic worldbuilding, premise, and concepts) before watching Fate Zero as it has relatively little handholding since it was produced with the assumption people who watch it are already familiar with the Fate franchise, however if you pay sufficient attention it shouldn't be a problem to watch it even without context.
It's always nice to see a doujin with a futa Douji having fun! I prefer Shuten Douji, but Ibaraki Douji is JUST as cute! I wouldn't mind to be pleased by either of them. Or made to please them. Here's to hoping this gets translated soon! Thanks SO much, Gigawatt!