The Japanese homonym of "ぉさん" is a respectful title for elder brother.
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Japanese nicknames for brothers:
Arnie-brother-Arnie-calls himself a brother to others.
Anic-Brother-Nicky-Any name, same as above.
Nini-にににに-nini-very intimate, usually used by children.
Ernitan-ぉたん-o Niyitan-ditto.
Nissan-my brother さん-Ni Ethan-is more respectful and used to address his brother directly.
Ernie sang-ぉさん-o You and I respect each other and call your brother directly or use it to call someone else's brother.
Ernissa-ぉ brother _-o ni I sama- is the most respected and generally not used. It is common to address your brother in Japanese calendars.
References:
Baidu Encyclopedia-Ounijiang