The grinding in the game is about repeating the same scenes over and over at a precise time of day with small increments in the scene content.
Like in Son of a Bitch, you go talk to whoever is the Kitchen at 8 AM, then spy on whoever is showering at 9 AM, then ... ... ... and you do this about 50 times for each scene before you get fap material.
While other games implement grinding by accumulating money or relation points in various random events or jobs, discovering new places, .. these games just make you go over the same place and scene ad nauseam. Because it matters less how much this person loves you, what matters more is how many times you went to the kitchen at 8 AM.