兄きょう弟だい分ぶん

noun

sworn brother; close buddy

Refers to a man who is like a brother through a pledge of loyalty, not by blood. Often used in yakuza or historical contexts, but can also describe a very close male friend.

• 彼かれは私わたしの兄きょう弟だい分ぶんで、何なんでも相そう談だんできる。

  He is my sworn brother, and I can talk to him about anything.

• あの二人ふたりは兄きょう弟だい分ぶんの杯さかずきを交かわした仲なかだ。

  Those two have exchanged cups as sworn brothers.