Seeing Yumi in the preview reminds me of something that I still don't quite get the logic behind after all these months: the infamous yumiknows flag.
This flag represents how much Yumi knows about Chika's relationship with Sensei (more specifically, Chika self-proclaiming to be his girlfriend), and determines her action at the end of
Matador.
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But to me, yumiknows at best can only represent whether she knows or not
by the time of the event Abyss, and Yumi would still have tons of chances to learn it from Chika off-screen afterwards, in the same manner as Route A (IIRC there wasn't a specific event that entails Chika telling Yumi).
So in order to make Route B work, Yumi would have to remain completely oblivious throughout the time from
Abyss all the way to
Matador.
Since there really isn't anything that prevents Chika from telling Yumi off-screen, the fact that Chika apparently just decided not to say anything to Yumi if
Abyss came first is what I find odd.
(note that there is no dialogue variation in
Zanzibar that checks yumiknows, so Chika should have the same amount of tendency to tell Yumi regardless of routes)