With this one simple trick she can lock you out of the game. Speedrunners hate her!
Since I don't want to spoiler the story, I'mma insert some blank lines.
It's possible to skip "one room" ahead in Team Yukari, getting Yuyuko to leave before sealing the door between the trains. (It's actually easier to achieve than you think.) Then you can farm for infinite Boundary Break while you're at it with no means of lowering it. Alternatively, you can really seal your fate by following Yuyuko to the graves.