I will try and explain the ranks as best as I can in the following way: There is kind a main tree trunk story branch that is the major path of the story. Right now there are two MAJOR paths: K4 and below (sub) and K5 and above (dom). So ranks for those major paths won't matter as much as a K5 and K8 will see the same major scenes.
There are smaller side branches that will lead to specific scenes. Ranks matters a little for extra flavor scenes. A K3 has seen one extra specific scene with Olivia err "watering" someone. Another example: to formally do a game shot host dom path with Katsumi later, you will have to have chosen the "gameshow" tag from 0.5, she also mentions in the story you need to be ranked K7 or higher to work that job. So at some point (not yet), a player needs to hit K7 to see that specific little branch from the perspective of Kane helping run the game show. (versus not) A few minor scenes such as what room/girl might appear in a small scene might matter for specific rank. For example in 0.5 update, a K5 saw one room and Chanel/Delilah kiss/play in front of you/Kwame, at K6 another scene with just Delilah happened (either just blowjob or sex depending if you had 2 points with her), and a K7 yet a third starting room with Junko (again either just blowjob or sex depending if romance path open with her). But after the start of 0.5, most of the dom scenes were basically the same.
So rank is not a gigantic difference at all for a lot of scenes. (too hard to write four entire story paths for say K5, K6, K7, and K8, etc.) In the end, the major endings are more defined by what big choices you make with certain decisions/women. A K6 won't be locked out of a major romance or ending possibility with the huge choices. Trying not to spoil, but hope this helps!
