He's not (at least I'm not sure yet) the word dongsaeng adresses younger men but also little brothers, just like noona adresses older sister and older women in general and just like Hyung adresses older men and older brothers
Or idk if that's a good example but they can address a non-binary person just like it can just be used to not specify someone's gender. You just have to know more context to know which is which
they are step brother
No it's his kohai.
okay
okay so it's his little brother