Ending 9 is a random chance
Well that's interesting. All the walkthroughs titled how to get ending 9 seemed to have it figured out. But I didn't read to the end because I didn't want more spoilers.
Guess I got lucky on my first shot. It just felt like there was more to do in that place where I managed to do ending 9. Maybe not. I guess I'll see if it randomly appears for me again.