Responses

Like oppa (korean) i get it, since it could literally mean big/elder brother or older male that could be used for older boyfriend/male love interest. Or else they use other nicknames like yeobo or smth. Basically thats reasonable.
But onii chan is... Is just older brother.
Plot armor is helping them out so good lmao just call him by his name and put kun or chan whatever why onii chann #-.-)
Okay yall can get together since there's no blood relationship.... But at this point stop calling him onii chan (⊙…⊙ ) no JUSt No call him something else but onii chan