Question for someone from Japan/Korea

Hi I'm writing a light novel that I'll put on YouTube . Most of the characters are from different country origins which have already been named. 

One of the heroes though is from Japan/Korea (it's a completely different world but similar)

I am stumped with how to name the character/address the character in different situations so if someone who knows could comment that'd be great.

Btw I already tried online but chatgpt keeps giving bad answers that contradict itself.