Something is definitely funky with Tsubaki's alt end. Watched a friend choose option 1 against Carl so he didn't fight him, then AHed Jin, regular finish against Noel, got the alt ending. I did the same exact thing and did NOT get the alt ending. Restarted, chose option 2 against Carl, beat him normally, AHed Jin, regular finish against Noel, then got the alt.
The fact that I did the same thing as my friend and we got two different endings leads me to believe there's some kind of random chance factor.