Well, they didn’t bother keeping the truth away for too long once it was made obvious. I have to respect that.
In this episode, the re-powered school has a lot of new students. It’s implied, though, that some of this may be due to the hot new teacher (our main character Natsuki, not Catherine) attracting students with other causes on their mind than studying. This doesn’t please Minamo, and while she’s willing to be quietly wistful about it, Ryuuji wants to give more of a push, supporting her interest in Natsuki. This leads to a bunch of the secondary characters banding together to try to extract an answer about what Natsuki’s love life looks like from him.
The answer seems to be that he hasn’t gotten over his first crush, a girl somewhat older than him who saved him when, after the accident that left him minus one leg, he was feeling rather suicidal. He doesn’t know where this girl is any more, or even what her name is, but she left an incredible impression through their largely unseen interactions.
He does, however, manage to provide a physical description, which causes the other characters to immediately think of Atri herself. Natsuki denies it, claiming that her personality was entirely different at the very least, but to get this out of the way only slightly faster than the show, it’s confirmed by the end of the episode: helping out with music class, Natsuki plays a song that was special to the girl in his past, and hearing it restores enough of Atri’s memory that she’s able to sing it and greet Natsuki based on their past connection.
I’ll be honest, it wasn’t a surprise even before “silky hair and red eyes” was given as our sign, from narrative logic alone. But just because something isn’t surprising doesn’t mean it isn’t a good way to go. Natsuki’s hangups regarding Atri are going to get a lot more complicated, as is the difficult line she treads between being a machine and being a person. Natsuki seems to already be homing on the idea that she has authentic consciousness and emotions, but you could question now if that’s what he wants to see.
At the same time, while Minamo may have hit the nail on the head that romance isn’t in Natsuki’s wants or needs at the moment, the talks around his feelings regarding Atri before the reveal lean to her being ruled out as a partner as a matter of course: she’s a humanoid robot and while a little math says their apparent age is supposed to not be that far off canonically, she is on the undesirably small side in his estimation. But how will that change now that she’s conflated with the girl who saved his life, literally and emotionally?
A little aside on the math: they say that Mystery Girl was four or five years older than Natsuki. This is when he was nine, which would make her 13 or 14. Before the reveal, they say she’d be 20 now, suggesting that Natsuki is 15 or 16, which I don’t remember being canonically made clear before. I suppose single years can matter a lot at that age.
Anyway, that’s enough out of me. The way this is deployed is as a setup with payoff pending. Since the mystery girl doesn’t remain a mystery for long at all, the real question is what do we do with this?