And one last question before I dive back to the game... is there 0% chance of pregnancy on Safe Days?
There is never a 0% chance of pregnancy on a "Safe" day. I have cum inside on a "safe day" on multiple play tests.
One test I went a week waiting for a pregnancy ending that never came.
A second test where I came inside her more than once, and sure enough, the pregnancy ending came after 3 days. (Triggers automatically after eating dinner on the third day.)
I suspect that the RNG rerolls every time you cum inside until the [pregnancy] flag is tripped. But since I can't see the mechanism working, this is only a guess.
If you want to cum inside without worrying about triggering the pregnancy ending (good or bad), you have to slip her a morning after pill in the [Have a Drink] menu, after the sex-scene, not before. Beware, you can only offer Imouto a drink once a day.
Edit: Unrelated, but is 1.9 supposed to have a toilet scene? Because on earlier releases, when Imouto drank almost anything, she would have to excuse herself to use the toilet.
My version of 1.9, downloaded from the link in an earlier page, and when she gets a drink, there's "...." for her dialog and the game immediately reverts to having Imouto wait somewhere in the room.
Thanks.