I have a story set in Japan with Japanese high schoolers (around the ages 17-18). One of them is called Kiwatamura (family name) Ryuko (first name). He is Japanese and lived there as a kid but he spent a few years in America recently. Since English speakers mostly call people by their first name he got used to being called Ryu or Ryuko by his peers. After he came back to Japan and enrolled in high school there with Japanase classmates he realized he still prefers being called Ryu or Ryuko. From what I read, classmates would usually call each other family names without honorifics, so the default would be Kiwatamura for his classmates. I read that sometimes nicknames are also okay. Would these change if someone was a transfer student (aka joining the school and class later but still being the same age).
If he expressed his preference to be called Ryuko to his classmates or kids his age he just met, would they call him that? Would they be actually comfortable using his first name since it was him who asked, or would they just do it to respect his wishes but still feel uncomfortable while doing it?
If he asked his peers to call him Ryu would that be something they would use as a nickname and would be comfortable using it? Or is it too close to his first name?
Would it be likely that in response someone would also tell Ryuko to call them a nickname or their first name? Or would this only happen after they became close friends?
I am looking for real life experiences so I could make the story a bit more authentic. Thank you for all your help!