I wouldn't know, and so I am fishing for someone who'd be able to definitely say "yes, Shu's a girl" or "yes, Shu's a guy" or "there's nothing in the Japanese verisons of these two chapters that could've hinted at any of that"
As a translator, I can tell you that there's absolutely no dead-giveaway hint
in the language about the gender of the character. The "chan" could be one, but, as I said, it's not absolute, depending on the relationship Aya has with them.
Japanese is like that. Speakers often totally skip the use of personal pronouns or, when talking about someone, they use their name and not "he" or "she". They use it mostly if they want to emphasize the gender, in which case they'll specify "kanojo" or "kare".
While Narita uses "Ore" (assertive masculine "I") often enough and so clearly identifies as male, the Shu character didn't use any gender specific pronoun or phrase turn that would allow anyone to say with certainty "it's a girl" or "it's a boy".
The only real hint is the somewhat bulging chest in some panels, which is why it's most probably a girl.
It often trips beginner translator, because they assume a gender and are caught later when it's not what they thought. It's also a surefire way to identity sloppy AI translations, because the models often default to male pronouns. I'm currently translating a "gender bender" and the first chapters were translated by someone who assumed the characters knew each other gender (or used a LLM), so put "he" and "she" in their mouths, but later in the manga the characters suddenly mulled about the gender of the other, which made the previous translation ridiculous.
