how did the mother address him? i'm guessing she didn't use they/them pronouns.
Mori addresses Yamori as he/him so....
Japanese doesn't really work that way.
First-person pronouns are what's more commonly gendered.
They don't use second-person pronouns very often. "That/this person" is common, using names...
You don't even say "you" as much as saying someone's name.
"I" is the most common pronoun to hear, and there are 52 different ones, and all signal different things.
It took me multiple years to settle on "uchi", to the point I didn't speak Japanese or even think in Japanese for a few years.