Aside from offering a glimpse to Yasu's past, there is something intriguing about how An Apple Each Day played out.
Two things happen: Yasu going over her own trip to the past care package, and Sensei losing connection to what Touka has to say.
What I think is intriguing is how orthogonal these two things can be, plus the unclear purpose of the divine intervention in the event (as if other divine purposes were ever clear), followed by the feeling that this event feels like to be pretty up for the readers and not for Sensei.
First, Yasu's flashback clearly is something only happened to her. Whether this kind of thing happened to her on a regular basis or not is unknown, but this isn't something that takes place so that Sensei could learn more about Yasu.
Next, Sensei didn't blackout. This isn't like those [redacted] where sensitive information is blocked by Sensei's mind; this time he more or less just kinda lost his hearing to specific parts of Touka's words, and he actively notices that as well.
What I think is intriguing is that since I don't believe Touka is lore-equipped enough to have something earth-shattering/world-breaking to say, and the fact that Sensei didn't blackout and didn't go through those flashbacks with Yasu, it isn't his connection being severed or his consciousness being redirected, it really is the readers'. It's ours (and somehow Sensei get affected by missing some parts of the conversation). But what in-game purpose is there? Yaus going crazy by her own terms from time to time, fine; but why blocking Sensei from keeping his conversation with Touka going?
Anyway, the whole thing feels like a LiL-style MEANWHILE screen transition from Sensei's perspective to Yasu's perspective. But I might just be nitpicking on how scenes play out, and there might not be a deep reason behind it.