Not setting 100% completion as a hard requirement is a solid choice, but what I mean is that fully training Suzune is the only way for her to discard her morals and modesty in front of her boyfriend. This is a process she must go through. Of course, if you want to unlock this feature faster, it's very simple: when the official version is released in 4 months, I will include a fully unlocked save file, so you can choose whichever playstyle you prefer.