Bought it yesterday as soon as it was released to support the author. To be honest, I shared exactly the same impressions after playing the trial, so this time I started the game after reading the previous releases from the circle (CGs and dojins) plus I'm proceeding more carefully with my reading. Luckily, the japanese level is on the easy side, apart from the usual old-men-talk from the grandfather.
Anyways... Given the way in which the main heroine easily surrender and accepts the conditions from the grandfather in order to investigate the mansion and protect the nun, it looks to me like either:
A) We have to take the previous releases as past "canon"
or B) Even if we don't do that the impression is that, like it happened in the first release from the author (
https://e-hentai.org/g/862926/418203fa94/), we have to take as the main heroine having already surrendered off-screen before the beggining of the story to the advances of the grandfather.
Maybe someone who has completed it can confirm if it's either A or B...in case there's a clear answer along the road.